This paper records an attempt to assess the prophylactic value of immune gammaglobulin, prepared from the serum of recently vaccinated adults, in the protection of close contacts of smallpox in Madras. The results serve to confirm findings of a previous study made in Madras in 1953, and show that the incidence of smallpox in close contacts given immune gamma-globulin prophylactically was about a quarter of that in the control contacts who received no such passive immunization-a statistically significant difference. Because of the limited supply of immune gamma-globulin, it is likely that its prophylactic use will be restricted to those especially at risk, for example, close unvaccinated family contacts, newborn infants and pregnant women.In a previous field trial of hyperimmune gammaglobulin for the prevention of smallpox'1 the number of cases involved was insufficient to give conclusive evidence of prophylactic value, although the results were highly suggestive. For this reason, the experiment was repeated in a co-operative venture involving the

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