Mycoplasma capricolum causes high morbidity and mortality in goats. Young kids fed a one-time oral dose of greater than or equal to 1 X 10(5) colony-forming units of the GM13 isolate usually died during the septicemic phase. The cardinal lesions were a fibrinopurulent polyarthritis and an acute, diffuse interstitial pneumonia. Lactating goats exposed to low numbers of the organism via the teat canal experienced similar lesions and acute mastitis, agalactia, and hardened udders. The intramammary inoculation of M. putrefaciens caused only mastitis; infection could not be initiated by oral, intranasal, or i.m. exposure.