A total of 1,278 strains of Streptococcus faecalis, 688 of Str. faecium and 796 of Staphylococcus epidermidis were collected from laboratory animals of 20 colonies in 1980, and tested for their resistance to 20 drugs. Thirteen percent of Str. faecalis, 12% of Str. faecium and 25% of Staph. epidermidis were drug resistant. Multiple drug resistant organisms were frequently detected in laboratory animal colonies where antibiotic treatment had been undertaken. TC-resistant streptococci and EM-resistant Staph. epidermidis were distributed in about half of the colonies regardless of the history of antibiotic usage.