Since the recent extensive domestication and farming of deer in New Zealand, tuberculosis (Tb) has presented a major health issue in farmed herds. The spectrum of disease pathology and immune reactivity in this naturally infected species represents a potentially valuable large animal model for the study of the underlying immunological and pathological mechanisms involved in Mycobacterium bovis infection and its spread. A combination of laboratory assays for the detection of tuberculosis in deer is described. Domesticated deer are genetically diverse and their exposure to natural variations in environmental conditions results in a spectrum of immune responses and pathology of Tb, similar to that found in man. The model has special relevance to the study of host responses to tuberculosis in immunocompromised individuals, particularly those in the third world. Elucidation of the mechanisms involved in immune responses to Tb in deer will facilitate the development of vaccines and improved diagnostic assays for Tb in man. © 1990, Academic Press Limited. All rights reserved.