Summary An account is given of a tuberculin survey of the child population of a city with a population of a quarter of a million. A fifth of the children under school age and 83 % of the school population were tuberculin tested in a year. Three out of 35 tuberculin positive children under school age and 7 out of 1,214 (6 per 1,000) unvaccinated school children with strongly positive tuberculin tests were found to be suffering from active tuberculosis. Thirteen out of 1,011 (13 per 1,000) adult household contacts of tuberculin positive infants and hypersensitive school children were found to be suffering from active tuberculosis.