The antimicrobial susceptibility of 277 strains of Yersinia pestis was studied using broth microdilution panel. In recent strains, trimethoprim, cotrimoxazole and ampicillin were the most active of the antibiotics tested (MICs less than 2 mg/l). All strains were inhibited by 16 mg/l of kanamycin and sulfamethoxazole, 32 mg/l of sulphadiazine and sulfanilamide, and 64 mg/l of sulfamethoxypyridazine. Doxycycline, minocycline, chloramphenicol, demeclocycline, tetracycline, oxytetracycline and chlortetracycline were equally active but some of strains were resistant (13% for tetracycline; 32.5% for oxytetracycline; 84.5% for chlortetracycline). Analysis of MICs in relation with time (comparison of the two period: 1926-1948 and 1948-1989) evidenced a trend towards a decrease in susceptibility to cyclines prime generation. Sulphonamides and streptomycin preserve the some efficacity on Y. pestis but we have to notice the possible existence of resistant strain on high level with streptomycin.