A 25-year-old black female heroin addict presented with Staphylococcus aureus endocarditis. Because of a history of penicillin allergy, therapy was gegun with cephalothin (Keflin); lack of clinical response led to the use of clindamycin. Response was excellent. After six weeks of treatment she was discharged well, only to return six days later with recurrent endocarditis. The organism, confirmed by sensitivity and phage typing, was identifcal to that causing the inital episode. This patient illustrates the apparent failure of clindamycin to eradicate a deep-seated intravascular infection with a sensitive organism.