In 1986, three seals died in a marine park in Western Australia; culture of postmortem tissue suggested infection with Mycobacterium bovis. In 1988, a seal trainer who had been employed at the Western Australian marine park until 1985 developed pulmonary tuberculosis caused by M. bovis while working in a zoo 3,000 km away on the east coast of Australia. Culture characteristics, biochemical behavior, sodium dodecyl sulphate polyacrylamide gel electrophoresis, and restriction endonuclease analysis suggested that the strains of M. bovis infecting the seals and trainer were identical but unique and differed from reference strains and local cattle strains of M. bovis. The infection in both the seals and the trainer had a destructive but indolent course. This is the first time that M. bovis has been observed in seals and the first time that tuberculous infection has been documented to be transmitted from seals to humans. Further investigation of the extent of tuberculous infection in seal populations elsewhere in the world seems warranted, and those working with seals and other marine animals should be monitored for infection.