The authors studied comparatively the sensitivity of 3 bacterial strains (P. Aeruginosa and two E. coli) with regard to antibiotics using an automatic method (ABAC) compared with a gel diffusion technic with impregnated disks. Each strain was tested by both methods 50 to 55 times. The diffusion method was easily reproducible with an average standard deviation of 2.23 mm. Its results were in agreement compared with the average diameter of measurements in 93.3% of cases. The automatic method gave results which agreed together in 95.7% of cases. It is thus reproducible. If one compares it with the results of the diffusion method, considered here as the reference method, we obtained the same response in 86.3% of cases. In 13.7% there was disagreement in interpretation (in most cases, the strain found intermediate in gel diffusion was considered sensitive on autoanalysis).