Six methicillin-resistant strains of Staphylococcus aureus isolated in Britain were examined for loss of resistance after storage for 30 mth at room temperature. Resistance to methicillin was lost from five out of six, to tetracycline from four out of six, to erythromycin from two out of four, and penicillinase from all five that were producers of it. The methicillin-sensitive segregants resembled the wild strains in bacteriophage-typing pattern, haemolysin production, Tween 80 reaction, pigmentation, and resistance to lysostaphin and to other antibiotics.