The aim of this study is to evaluate direct and standardized antimicrobial susceptibility testing methods for the detection of bacteria isolated from automated blood cultures. In accordance with the protocol of the study, 126 blood cultures were collected from the patients during a 12-month period in 2001-2002. The samples from positive bottles showing growth of Gram-negative bacilli or clustered Gram-positive cocci, determined by Gram staining, were used for direct inoculation onto Mueller Hinton agar. The negative smears which had positive cultures and the positive smears which showed mixed cultures were excluded from the study. The results of direct disk diffusion tests were compared with those of standard Kirby-Bauer disk diffusion method, and discrepancies were classified as very major, major, or minor errors. The overall agreement of the two methods for Staphylococcus aureus and coagulase-negative staphylococci, in terms of the interpretive categories (susceptible, intermediate, and resistant) were 92.2 % and 90.7%, respectively. There were 32 (2.5%) very major errors, 16 (1.3%) major errors and eight (0.6%) minor errors which were caused by the direct method for Staphylococus spp. The overall agreement of the two methods for Enterobacteriaceae and Pseudomonas spp. in terms of the interpretive categories were 92.1% and 96.8%, respectively. There were 22 (1.5%) very major errors, 11 (0.7%) major errors and 19 (1.3%) minor errors caused by direct method for Gram-negative bacilli. The rapid method for the antimicrobial susceptibility testing of Gram-negative bacilli and oxacilline resistant S. aureus is simple and requires no centrifugation, preincubation, or standardization of the inocula. This method can be used for patients with bacteremia. The direct disk method is proposed as a test that can be used as a supplement to the standardized procedures for the earlier determination of the susceptibility patterns of aerobic Gram-negative bacilli and Staphylococcus spp. from blood cultures.