I agree with CA, no underwear with the Tri-shorts.

In my mind, a tri-suit is just a more multifunctional version of a swimsuit and since I don't wear a bra and panty under my training swimsuit, why would I under my tri-suit?

I also learned early on when I started running (my primary sport) that underwear only do one thing when exercising, go for the crack.

If the idea of not wearing anything doesn't sit well with you, I suggest going with a sport thong. A thong knows where it's supposed to be and doesn't go anywhere but there. I run in them often and they are great.

Hopefully the tri-suit top you have has a support/sports bra in it. But again like, CA said if you are well endowed you may need something more.

This is the tri-top I have and I'm really pleased with the upper support.

http://www.teamestrogen.com/products.asp?pID=24648

The one thing I really like about Zoot too is that all the seams & fabric are super soft, so while something might have a lot of support you aren't stuck with scratchy wet material on your skin.

Hope this helps!