SUMMARY AND INTRODUCTION: Although bacteria are visible in Gram-stained smears of rumen entodinomorphid protozoa, no successful attempts to culture these bacteria have been reported. Gutierrez & Davis (1959), using oligotrich protozoa from the calf rumen, cultured 3 to 10 Streptococcus bovis per protozoon, after disruption by crushing between glass slides. The purpose of the present study was to investigate the viable bacterial flora of Entodinium caudatum which had originated from the sheep rumen, and had been maintained under constant conditions in vitro for over 6 years (Coleman, 1958, i960). Part of the work has been reported previously (White, 1966).