Of 19 cases in which the history seemed typical of hemolytic disease and yet in which no anti-Rh had been detected, the incomplete antibody (anti-Rh standard) was detected in 6; of 26 cases in which a trace of anti-Rh had been detected, the incomplete antibody was found in 19. No evidence was found in 100 tests for the presence of incomplete forms of the other 3 types of anti-Rh agglutinins.