Note sure if this is the same place, but try here:

http://www.mpg-paris.com/eng/index.html

The shop is called Maitre Parfumier et Gantier and it is modeled after a 17th century French perfumier. Address is 5, rue des Capucines, 1e. The atmosphere is stunning (crystal chadeliers, period furnishings), the perfumes are made on site, and the ability to sample all of the scents from crystal bottles was alot of fun. A big step up from sampling in a department store and the prices were reasonable.

Thank you ParisEscapes. The store I was thinking of actually had different scents that you could blend to come up with a 'personalized' perfume.
I have made a note of the Maitre Parfumier as it definitely looks like a shop we'd enjoy visiting.

Maybe kamark is talking about Sephora's?? Does anyone know the address? (it is on the Champ Elysees I think).

There is a Saphora's on Rue Rivoli as well.

Sephora is more of a perfume and cosmetics department store, i.e. LOTS of brands and ability to try without salespeople hovering. There are a number of them in major cities in the U.S. now.

ParisEscapes -- thanks for the recommendations for the customer prfume sho (I am a perfume junkie.) I know of a few shops, but all are quite expensive for custom efforts.

I was just in Paris and noticed several places that do this. Guerlain on the Champs-Elysees does this, for one place. There are Sephoras all over Paris now, probably at least 10, and in very ordinary places (like les Halles). However, they do custom mix various products -- and perfume is one of them, as I recall. At least in their flagship store at 70, Champs-Elysees, which is where I'd go.

I used to be in the perfume and cosmetic business, and actually think making scents is really something that should be left to professionals. They can do it a lot better than an amateur.

Thank you all for your replies. I agree with the comment about leaving the blending to professionals except that this is a trip with my 16 year old daughter and I thought it would be a great learning experience for her, not to mention fun, to pick her own 'ingredients'. The only souvenier I'm planning to bring home for myself this trip is a nice bottle of perfume and for that I will definitely be buying 'premade'.