Four antibiotic surveys were carried out in a teaching hospital within the framework of an intensive drug monitoring system during 1976-1978. The proportion of inpatients receiving antibiotic therapy at any one time varied from 25% to 32%. Penicillin, ampicillin and co-trimoxazole were the most frequently used antibiotics. The use of cloxacillin increased over the survey period. Approximately 85% of presumed infections were treated before the results of microbiological tests became available. Between 29% and 39% of all courses of antibiotics were given for prophylaxis of infection. Between 13% and 30% of patients received more than one antibiotic concurrently; indication for such combined use appeared inadequate in 31% to 80% of courses.