BOSTON — Walgreen Co. and CVS Caremark Corp. were among the top 25 most-trafficked retail web sites last month and, as in the brick-and-mortar arena, the chains are battling it out for online customers, according to online marketing firm Compete.

In July, Walgreens.com came in No. 15 among retail web sites, with 7.56 million unique visitors, up 5% from June and 34% from July 2008, reported Boston-based Compete, a unit of TNS Media.

CVS.com, meanwhile, finished No. 25 but posted stronger growth. The site had 5.04 million unique visitors in July, a gain of 15% from the prior month and a 103% jump from July 2008.

"Both CVS.com and Walgreens.com saw their traffic rise month-over-month, but CVS.com’s growth outpaced that of its rival 15% versus 5%," Compete stated. "Although Walgreens.com continues to maintain a sizable online lead over CVS.com, the CVS.com site has narrowed the gap of late.

"And CVS.com traffic has risen 103% year-over-year since the site was relaunched last summer. Stay tuned for this ongoing competition for pharmacy visitors," the marketing firm said.

Compete said that each month it examines the top movers in one of 225 industry categories. The company noted that month-over-month traffic gains for individual web sites can be a direct result of specific marketing or advertising campaigns.

Other mass retail chain sites in the top 25, all of which operate pharmacies, included Walmart.com (No. 2), Target.com (No. 3), Kmart.com (No. 12), Costco.com (No. 14) and Samsclub.com (No. 19).