The API 20A System was tested in 3 modifications. The microtubes were inoculated with the API anaerobe basal medium, filled up completely with sterile mineral oil and incubated aerobically. The test strips were inoculated with the basal medium and incubated in an anaerobic chamber. The strips were inoculated with a modified Viande-Levure medium containing Tween 80, vitamin K3 and hemin. The microtubes were covered with sterile mineral oil and incubated in an anaerobic chamber. Each procedure was compared with the conventional method (PRAS). The overall agreement between the 3 modifications of the API System and the conventional method was 83.2, 91.7 and 98.5% related to the number of tests performed. The advantage of the modified medium was also demonstrated by measuring the growth rate of some anaerobes in thioglycolate broth, API basal medium and VL-medium, modified as mentioned above, nephelometrically. So the micromethod is more accurate and reliable when inoculated with an improved medium.