Transmission of bovine brucellosis from dam to offspring under natural circumstances was demonstrated in a 2 1/2-year study of an infected cow and her calf. The cow delivered a full-term heifer calf after her first gestation. The calf remained with its dam until 7 months of age, then was placed in isolation until bred. During her first gestation, the second-generation heifer became seropositive for Brucella abortus. She later gave birth to a calf with B abortus infection, as determined by isolation of B abortus biotype 1 from stomach contents, heart blood, lung, and spleen of the calf. The same organism was isolated from the placenta and milk of the dam.