Ok, here goes, I'm not sure which one does the most. I started on them one at a time and saw moderate results from all three. It was when I combined them that things really started happening. I know from research that Tribulus is sketchy at best. Form what I understand, it will only help if you need help, which is why most of the studies show no improvement, because most of the studies have been done using healthy young men. As far as my background: my problem is different than most guys here. I had a prolactinoma. I'm not a very good poster so I don't know how to post the link, I have another post called "prolactinoma experience" on one of the other boards. But, I started going into ED when I was in my late 30's. About that time I also started having headaches 24/7. But because I'm a migraineur my Dr.'s didn't look any further. So I spent a few years on antidepressants and anti-anxiety meds, and lots of pain meds. When I was 42 after a nerve racking honeymoon with my second wife, my Dr. put me on Viagra without an exam of any kind. Said it was my age. Well, it worked, but with consequences. Always get a migraine when I use it. So, for years I've been searching for a better solution. I am now 55 years old. Had my surgery to remove my tumor about 2 years ago. Have been on test. injections ever since. My Urologist actually found my tumor after Androgel quit working and decided to test my Prolactin level, which was way high. So I still use Viagra, but the supps listed above make things work alot better. As I said, I've not had a morning woodie for about 20 years, until now!