Petri dish covers made of aluminum, to be used in place of glass or porcelain, are proposed. The metal cover would be used to replace glass covers, the same type top with an absorptive disk to replace glazed porcelain tops, and a metal cover that has had its center removed and containing an absorptive disk to be used instead of an unglazed porcelain cover. Concn. of the medium, due to moisture loss from the agar, is the same in comparable aluminum-glass or aluminum-porcelain covers. These covers are unbreakable and cleaning problems are greatly simplified. No toxicity has been encountered in the proper use of these covers and disks.