In a 1-year prospective study 83 children, who had been in close contact with 52 adults who had tuberculosis, were examined. Thirty-six of the index cases had culture positive tuberculosis and 16 of these had smear positive tuberculosis. All the children had been BCG-vaccinated at birth. Forty-one (49%) of the children were PPD negative on examination with the Mantoux test. Of these 83 children, one 14-year-old boy was diagnosed as having primary tuberculosis and was treated. Twenty-one children received INH therapy, 12 because of their age (under 2 years of age or at puberty), nine because of a strong positive reaction to the first Mantoux test or because of the conversion of a negative test result to positive during the follow-up period. Seven of the latter nine children had been in contact with persons whose disease was culture- and smear-positive. It is concluded that as the frequency of tuberculosis declines, the practice of examining all children who have been in close contact with tuberculous adults is possible. The children who have been in contact with smear-positive index cases are at special risk of contracting tuberculosis.