Internet pharmacy PlanetRX Inc opened its virtual doors for business yesterday and took the opportunity to announce a promotional deal with Yahoo! Inc. The marketing agreement, for which financial terms were not disclosed, will see PlanetRx’s products accessible through merchant buttons and banner advertisements on Yahoo’s health-related pages and throughout the Yahoo network. The two companies also plan to run several promotional campaigns.

Not to be outdone, rival Drugstore.com – which has funding from internet retailing giant Amazon.com – announced a similar alliance with a portal partner, having inked a deal with Excite Inc that will have its site promoted on certain Excite portions of Netscape’s Netcenter. The two will also run additional promotional campaigns on Netcenter. Drugstore.com already has a deal with Yahoo and will battle it out with newcomer PlanetRX for market share there, much as the two companies will on the America Online Inc network. AOL has taken money from both for the privilege of sitting side by side in the pharmacy area of its web site.