RESUMEN
When a Korean child is living in close contact with a person with active pulmonary tuberculosis, the risk of his acquiring the disease is great. In seeking an effective means of reducing this risk to the chi1d, isoniazid was given as secondary chemoprophylaxis to 233 tuberculin-positive children under 5 years of age who were clinically free of disease but were living in close contact with a household member with active tuberculosis. The condition of these children after 9 to 12 months of chemoprophylaxis was compared with a similar control group of 216 children living under exact1y comparable circumstances. An analysis of tile results of this study indicates that secondary chemoprophylaxis with isoniazid is effective and worthwhile for children under 4 years of age who are under constant exposure to tuberculosis. That there was such a protection is indicated by the fact that (1) isoniazid markedly reduced the size of the tuberculin reaction and that (2) only 2 children receiving isoniazid developed active tuberculosis (0.8%) as against the 8 controls who did (3.70%). The faithful cooperation of parents in administering prophylactic isoniazid to small children is often difficult to obtain. This difficulty is suggested by the fact that in the case of the 2 children in the isoniazid test group who developed active tuberculosis, the actual drug intake had been irregularly given and amounted to less than half the prescribed dose.