The mechanisms of humoral and cellular immunity in the body's defences against tuberculosis are reviewed in the light of recent fundamental works. Major progress has been made in understanding the structure of mycobacteria, in particular in those areas concerning antigenic determinants which may have diagnostic or therapeutic implications. The impact of the human immunodeficiency virus infection on the antituberculous defences is discussed, on the epidemiological aspects as well as clinical and physiopathological.