1. Studies of the Rh factor in 11,486 pregnant female American Negroes revealed 1,302 who were Rh0 negative (8.4 per cent). Sixty-four cases of isosensitization were encountered which gave an incidence of 4.9 per cent in the Rh-negative patients. In comparison, among 8,889 Rh0-negative Caucasians, 460 cases of isosensitization (5.2 per cent) were encountered. The difference was found to be statistically insignificant.
2. Two typical examples of erythroblastosis fetalis in American Negro infants are presented.