Strains of Mycobacterium tuberculosis were obtained from 65 patients with pulmonary tuberculosis resident in Uganda, and from pulmonary and extrapulmonary tuberculosis in 42 British patients of European ethnic stock and in 67 Asian immigrants, often from Uganda, resident in Britain. The bacteriophage-type patterns of the African, British and Asian strains were different. The pattern for the Asian strains resembled that found previously in patients from South India, suggesting that there has been little interchange of organisms between the Asian community and the African and British communities alongside whom they have lived. The patterns for pulmonary and extra-pulmonary tuberculosis were similar. Strains of bacteriophage type 1, mainly obtained from Asians, were characterized by a greater susceptibility to the bactericidal activity of hydrogen-peroxide and/or a greater sensitivity to thiophen-2-carbonic acid hydrazide than strains of other types.