Pycnogenol is one of several supplements that has good evidence for its ability to improve erectile dysfunction. Pycnogenol, a patented water extract from the bark of specific type of pine tree in southwestern France, is a Nitric Oxide “booster”. Of course, many foods are erection-promoting Nitric Oxide boosters. Pycnogenol, while not a food, is an example of another plant-based blood flow builder.
According to history, Pycnogenol got its start from a group of French sailors who were nursed back to health from pine bark prepared by the local natives (I believe along the St. Lawrence in Canada). Regardless of how true the story is, the natives were probably centuries ahead of their time as pine bark is loaded with antioxidants and other remarkable phytochemicals. Pycnogenol has had stellar research results, including its ability to pump up your erectile strength. (See also How To Improve Erectile Dysfunction Naturally through foods.)
The study that put pycnogenol on the map in the fight against erectile dysfunction was one where a cohort of men (with erectile dysfunction of course) were given a combination of 1.7 G L-Arginine per day along side 2X40 mg doses of Pycnogenol.  L-Arginine is also a Nitric Oxide booster and the study showed that the two in combination significantly improved the erectile dysfunction of most of the men involved in the study. Several follow up studies have shown that varying combinations of Pycnogenol (40-120 mg daily) and L-Arginine (1.7 – 3.0 grams daily) result in 70-90% of men having restored erections and with no side effects. 
So how does Pycnogenol work its magic and improve erectile dysfunction?? It’s primary pathway is probably by directly boosting Nitric Oxide as mentioned above. A 2007 study found that 180 mg daily of pycnogenol increased arterial expansion by 42 percent in young healthy males that were actually given an inhibitor of L-Arginine.  This means that Pycnogenol led to significant release of Nitric Oxide and that is exactly what you need to improve your erectile dysfunction.
Second of all, one recent study showed that patients taking 200 mg of Pycnogenol per day for just five days reduced several key markers of inflammation.  A study from the same year found that Pycnogenol inhibited the COX-1 and COX-2 inflammatory enzymes. 
It is worth noting that COX-2 inhibition was the goal of the NSAID drug Vioxx that was pulled off the market by Merck: it did cardiovascular damage to around 140,000 seniors during its infamous tenure by causing increased fluid retention and high blood pressure. Many of these individuals could have taken Pycnogenol which is now a clinically proven osteoarthritis-fighter.  156 patients with knee osteo-arthritis were given 100 mg of Pycnogenol for three months and experienced an average 56% reduction in symptoms including pain reduction, improved ability to exercise and decreased edema.
Fourthly, sometimes venous insufficiency – a sort of Leaky Vein Syndrome – is one of the root causes for erectile dysfunction. One study found just that: 12% of patients studies had documentable venous insufficiency.  Pycnogenol has been found to greatly help those with, at least, advanced venous insufficiency. In fact, it was so powerful that at a daily dose of 150 mg, it actually beat out a medication typically prescribed for this condition. 
Also, if you already have high blood pressure, Pycnogenol has been found to help protect you from the damage that it does to your heart.  High Blood Pressure is very hard on many parts of the body, including the brain and various organs including the heart. Pycnogenol has also been shown to protect people with Blood Pressure from the edema that sometimes results from their medications.  In other words, Pycnogenol may not only help you to improve your erectile dysfunction, but it may buy you time to get to the root of your Blood Pressure problems.
The only downside to Pycnogenol is that it is patented, which tends to keep the price higher than many supplements. This is good, because the company apparently very carefully watches quality control which shows in their stellar research results. You can also save quite a bit by going through an online discounter such as Amazon: TwinLabs Pycnogenol Capsules, 50 Mg, 60-Count Bottle.
If you want to follow what was done in the studies, just couple between 1 and 3 of the above tablets daily (50 mg – 150 mg daily) with about 1.5 grams of L-Arginine. You can get L-Arginine very reasonably at either Walmart or Amazon: L-Arginine (500mg).
I do also want to mention that Pynogenol is very likely skin protective as well. Collagen is the backbone, if you will, of your skin and Pycnogenol has been shown to protect and even reconstruct collagen fibers in aging or damaged connective tissue. Pycnogenol also reportedly protects Vitamin C, which is also a collagen rebuilder. So Pycnogenol will not just help improve your sex life through improving your erectile dysfunction – it will also very likely improve your already dashing good looks while it is at it.
By the way, a hot tip that you can pass on to the woman in your life and score a few points is that pynogenol has been found to relieve the symptoms of menstruation at least in one recent study. Much of the pain associated with menstruation is believed to be associated with inflammation and Pycnogenol, 30 mg twice daily in this case, helped significantly with this woman’s issue. 
CAUTION: The only caution that I have about Pycnogenol is that the studies all couple it with L-Arginine, which has some potential issues. However, the dosages of L-Arginine used in the Pycnogenol erectile-dysfunction studies are all relatively low dose (1.5 g – 3.0 g). Read my link on L-Arginine for more details.
NOTE: Some studies have shown L-Arginine helps directly. Still other research with L-Arginine have produced lackluster results. For example, one study of healthy males showed no increased blood flow from 20 g/day, which is a very large dosage . Similar results were achieved in patients were discovered in patients with heart failure as well.  So the bottom line seems to be that L-Arginine, to work effectively, need a solid Nitric Oxide booster.
1) J Sex Marit Ther 2003 May-Jun; 29(3):207-213
2) J Inflamm (Lond),2006 Jan 27,3:1
3) Biomed Pharmacother,2006 Jan,60(1):5-9
4) J Phytotherapy Research, April 2008, 22(4)
5) Amer Journ Clin Nutr 2006; 83:780-787, 2006
6) J Reprod Med, 2004, (49)10:828-832
7) Hypertension Res, Oct 2007, 30:775-780
8) Cardiovascular Toxicology, March 2007,7(1):10-18
9) Clin and Appl Thrombosis/Hemostasis, 2004, (10)4:373-377
10) Urologe A, 1989 Jan, 28(1):48-53
11) Clin and Appl Thrombosis/Hemostasis, 2006, (12)211) Clin and Appl Thrombosis/Hemostasis, 2006, (12)2:205-212. See also Phytomedicine, 2000 Oct, 7(5):383-8.
12) Journal of Cardiovascular Pharmacology, Jul 1996, 28(1):158-166, “Effects of In Vivo and In Vitro L-Arginine Supplementation on Healthy Human Vessels”
13) J Am Coll Cardiol, 1996; 27:1207-1213, “Dietary supplementation with L-arginine fails to restore endothelial function in forearm resistance arteries of patients with severe heart failure”