Bacteriological examination was made on 64 bovine pneumonic lungs collected over a period from April 1973 to March 1974, and consisting of 50 from a slaughter-house in Sendai City, Miyagi Prefecture, and 14 from several outbreaks of so-called calf pneumonia in Tochigi Prefecture. T-mycoplasmas were isolated from 43 (67%) of the 64 affected lungs. The positivity rate was considerably higher (33/38, 87%) in year-old calves than in older animals. It was suggested that these T-mycoplasmas might not be related to human T-mycoplasmas serologically and that there might be several serotypes among T-mycoplasmas isolated from bovine pneumonic lungs in Japan. Mycoplasma bovirhinis was isolated from 19 of 38 year-old calves (50%) and from 6 of 26 older animals (23%). Film-and-spots producing mycoplasmas were isolated from 6 lungs and identified as Mycoplasma bovigenitalium. Pasteurella multocida, Corynebacterium pyogenes and Haemophilus spp. were detected in 44, 22 and 17 percent, respectively, of the 64 lungs examined.