Summary: Two similar micro-organisms with the characteristics of the order Mycoplas-matales were isolated from the eyes of calves with conjunctivitis. Both isolates produced only a slight pH decrease in broth and did not ferment glucose or hydrolyse arginine or urea -- hence they were almost undetectable by fluid cultures. Other biological characters included sterol dependence, indicative of the genus Mycoplasma, production of film and spots, growth at low temperature (20°C) or low pH (4.7), and failure to reduce tetrazolium. The two strains were serologically indistinguishable from each other, but distinct from known bovine and other Mycoplasma species tested. Because of their distinct biological and serological characteristics they are proposed as forming a separate new species, Mycoplasma verecundum, with strain 107 (nctc10145) as the type strain.