THE close association of tuberculosis in man with infection in the domestic animals was elucidated in the 1880’s and the elimination of animal-associated reservoirs of infection remains an essential element in the control of this zoonosis. Difficulties associated with the eradication of the disease in animals include the lack of a dependable diagnostic procedure for use in the companion animals, and the high prevalence ofMycobacterium intracellulare infection in British and Irish cattle which renders the interpretation of the comparative tuberculin test in that species more difficult. Also, the nature of tuberculosis in cattle differs significantly from that in man in that in the former species the diseased animal remains infected for life and is likely to be an “open case”, and as a source of contamination for other animals and its environment. Identification of the prevalence ofM. bovis infection in human patients would serve to identify new foci of infection in animals and would heighten public awareness of the zoonotic nature of this disese.