The amount of additional antibiotics measured by defined daily dose (DDD) methods after 2651 hip and 362 knee replacements was assessed after prophylaxis with one or three doses (1502/1511 patients) of cefuroxime. No differences were observed between the two regimens with respect to total amount, type, indication, and duration of additional antibiotics. The incidence of joint sepsis did not differ significantly between the two trial arms, but the sample was too small for definite conclusions. There were 11.4 DDD/100 bed days of additional antibiotics used in 21% of patients after hip replacement and 15.7 DDD/100 bed days in 31% after knee replacement. For wound problems, 3.8 and 6.9 DDD/100 bed days were given in the hip- and knee-replacement groups. For distant infection, 6.5 DDD/100 bed days was administered in both groups. Duration of therapy varied only in relation to indication. Prescribed were penicillins (43% to 50%), sulfonamides (18%), cephalosporins (10% to 16%), and nitrofurantoin (8% to 13%); drug use was related to the type of infection.