Predictive indices for the outcome of measles were sought from a clinical and immunological study. A poor outcome was defined as death or persistence of bronchopulmonary disease 6 weeks after onset. The 47 Black children studied were well nourished and lymphopenic (absolute lymphocyte count less than 2 000/mm3) in the first 2 days of the exanthem. The latter feature has previously been shown to carry a poor prognosis. Eight of the children recovered fully, 5 died and 34 had residual lung changes at 6 weeks. Other factors which could be related to prognosis in this group of children already at risk of severe disease were more extensive pneumonia and normal or minimally reduced serum complement C3 levels early in the course of the disease. A less than twofold rise in haemagglutinin-inhibiting antibody titre was also associated with a poor prognosis.