The two largest U.S. drugstore chains posted stronger-than-expected sales results in August.

Walgreen

(WAG)

had a 10.6% gain in same-store sales, or sales at stores that were open for at least a year, compared with the same month in 2005. Wall Street analysts, on average, had expected a 9.2% increase, according to consensus estimates reported by Thomson First Call.

The drugstore chain's total sales rose 17.2% in August to $4.2 billion, powered by 72 new store openings, including 12 relocations.

Same-store sales, or comps, for the company's pharmacy business rose 13%. Front-end comps increased 6.3%. At the end of the month, the fast-growing pharmacy chain was operating 5,461 drugstores.

Walgreen's chief rival

CVS

(CVS) - Get Report

reported that its comps rose 8.9% in August, compared with the same month last year. Analysts were expecting a 7.6% increase.

CVS said total sales rose 23.4% to $3.4 billion for the month. Comps for its pharmacy business were up 10.3%, while front-end comps rose 5.8%.

The company's comparable sales results don't include the 701 standalone Sav-On and Osco drugstores it acquired in June. At the end of the month, CVS was operating 6,163 retail and specialty pharmacy stores.

Shares of Walgreen were recently up 13 cents, or 0.3%, to $49.96. CVS was adding 43 cents, or 1.3%, to $34.38.