Use oxacillin (Sigma O 1002) in place of methicillin. It's more stable in solution to boot. J. Owen McCall, Ph. D. owen.mccall at abbott.com Anti-infective Research Dept. 47P, Bldg. AP9A voice: (847) 937-7957 Abbott Laboratories 100 Abbott Park Rd. fax: (847) 938-3403 Abbott Park, IL 60064