A five-hour protocol was compared with routine methods for identification and antibiotic susceptibility determination of bacteria from clinical specimens. A total of 9551 urine, wound, sputum, and throat cultures were processed using both procedures. The identifications reported less than 24 hours after the laboratory received the specimen were comparable to those obtained by routine methods for 87 to 95 percent of the Enterobacteriaceae, 90 percent of the staphylococci and enterococci, but less than 50 percent of the unusual species such as Providencia, P. maltophilia, or Acinetobacter. Susceptibility test results were reported after five hours' incubation for 97 percent of all stains examined except for P. aeruginosa where early results were obtained for only 71 percent of the strains. This protocol allows bacteriologic identification and antibiotic susceptibility determination within 24 hours of specimen receipt; therefore, appropriate antibacterial therapy for the patient's immediate needs can be started in a shortened period.