There a few possible causes for this. Is the flower getting more brighter/or direct sun than it did at the nursery(wherever it came from)? It could be dropping buds due to acclimation stress. It has to get used to its new eviornment and may drop flowers until it gets used to your place.
Other reasons could be under or overwatering. Passies like to dry out a little before you water them again.
Bugs could be sucking the flower buds and can cause drop. A few culprits are plant bugs (they look like squash bugs), aphids, and thrips. Look inside one of the dropped flower buds and on your vine very carefully to see if you see any.

Hope you can find out what's wrong with them.
~SJN

What kind is it?? Did you replant it??? Is it too wet?? Could just be struggeling(sp) to adjust to new conditions..
Chena

Thank you both for your input. I'm thinking it may be the change of environment. It was indoors at the plant sale, and I brought it home and put it on my sunny back deck. I have not replanted it yet, not sure whether to keep it on the deck or put it in the ground. The label just says Passiflora. It has the light purple blooms (if and when they open(: I'll be keeping a sharp eye on it because it was pretty expensive and I'd hate to lose it.

It's probably the direct sun that's causing it to go into shock. With new passis that have led a pampered life, its often good to introduce them to the great outdoors by setting them in partial shade for several days to a week before giving them full sun. The good news is that bud and leaf drop isn't uncommon, and the plant will regrow more sturdy replacements shortly. Be careful you don't over-water, though!

Thank you Jb, I will heed your advice.