During a two-week period, all inpatient bacteriologic culture reports (1,381) were monitored, and ongoing chart review was conducted for all newly admitted patients (436) who had cultures taken; 17% of the infections had no cultures taken when indicated. The average bacteriology laboratory cost to each of these 436 patients was$37.16. Total antimicrobial drug costs were estimated to be $41,700. Of cultures ordered for suspected infections in the medical and surgical services, 24.5% yielded positive results. Patients were already taking antimicrobial drugs when one third of the cultures were obtained. Immediate Gram stains were done 3.5% of the time. In only 20.9% of positive cultures with one or more isolates, 1.4% of negative cultures, or 7.0% of all cultures was a change made in therapy. There was no consistent logical approach to the use of bacteriological culture results.