After B.C.G. vaccination of a group of tuberculin-negative children in West Bengal, India, 197 have been retested with tuberculin. 35-5% showed a definitely positive reaction. Only 15% showed no response to B.C.G. When compared by weight for age, the rate of positivity of those below 60% of the Harvard standard was significantly lower than of those above 80%. Those between 60 and 80% were similar to those above 80%. However, when the group was subdivided according to protein and calorie nutrition as measured by arm muscle and fat cross-sectional areas, the difference was striking. The tuberculin-test response was grossly impaired in those who were primarily severely protein deficient (kwashiorkor type), significantly depressed in those who were both severely protein and severely calorie deficient (marasmic-washiorkor type), and not depressed in those who were severely calorie deficient but normal or low in protein (marasmic type). It is suggested that clear distinction between different types of nutritional deficiency in a given geographic area is of direct relevance in planning mass vaccination programmes in that area.