Patients with nephritis and schoolchildren in South Trinidad were surveyed for the presence of Corynebacterium diphtheriae in throats and skin lesions. The incidence of positive cultures was higher in skin lesions than in throat cultures. None of the children experienced symptoms of systemic intoxication. Subsequent to the increase in cutaneous infections, however, the incidence of symptomatic nasopharyngeal diphtheria also increased in Trinidad, suggesting that the skin lesions constituted an important reservoir of infection. One group of schoolchildren was reexamined after six months, and levels of antitoxin in serum were correlated with the presence of C. diphtheriae in skin lesions and throat cultures. The high levels of antitoxin observed apparently resulted from natural immunization in the absence of clinical signs of diphtheria. No effect of C. diphtheriae was noted on the colonization of skin lesions by streptococci or on the incidence of acute glomerulonephritis in the population.