The prevalence of Mycoplasma ovipneumoniae (MO) in three Communal Lands flocks of goats on the outskirts of Harare is described. In a single sampling of nasal swabs from 172 randomly selected, apparently healthy goats, 112 animals were identified as carriers of MO. The three flocks had a history of occasional deaths, following chronic and subacute pneumonia associated with isolation of MO as the only identifiable pathogen. Attempts to induce clinical pneumonia in groups of 6 to 8-week-old kids and lambs with local isolates of MO were not successful. However, MO was consistently cultured from the trachea, lungs, lymph node and thymus of some test animals. Cuffing interstitial pneumonia was also observed in these animals. Infection of the thymus occurred; this has not previously been reported with any Mycoplasma sp. The animals did not produce detectable serum antibodies to MO nor were they reactive to MO antigen in a tuberculin-type hypersensitivity test. The possibility that a state of immunotolerance may have been responsible for failure to develop clinical pneumonia is discussed.