In using immune adult blood serum in the prophylaxis of measles, we observed that the interpretation of our results depended largely on whether certain epidemiologic factors were taken into account. Under relatively constant conditions the results obtained in institutional exposures seemed good; the percentage of complete protections was high, whereas under similar conditions, with the exception that the children were exposed to their sick siblings at home after prophylactic treatment, the percentage of protections was very much smaller. We have therefore divided 263 cases treated with immune adult serum according to the circumstances of their exposure to measles in an attempt to answer the following questions:
How do the results obtained with serum injected prophylactically into children exposed to measles in institutions compare with those obtained under similar conditions in private homes; that is, in children exposed to their sick siblings and treated at home?
Can this difference