DEERFIELD – Walgreen Co. took another step Thursday in its push to grow through acquisitions when it announced the $438 million purchase of a regional chain that operates USA Drug, Super D and May's drugstores.

The Deerfield company also said monthly sales fell once again in June, as a split with pharmacy benefits manager Express Scripts Holding Co. continued to hurt business.

Walgreen plans to buy 144 stores in a chain focused on the mid-South from the privately held Stephen L. LaFrance Holdings Inc., which is based in Little Rock, Ark.