Anti-D immunoglobulin is an effective prophylactic against rhesus isoimmunization. It is generally regarded as ineffective once antibody production has developed though there have been a number of inconclusive reports suggesting it may suppress early sensitization. Anti-D (100 micrograms) was given after delivery of a rhesus (D) positive child to a rhesus (D) negative mother who was shown to have anti-D antibodies at that time by five tests on two separate specimens in two different laboratories and by a weakly positive direct anti-globulin test on the cord blood. In a further pregnancy with a rhesus (D) positive child no antibody was detected by multiple tests including enzyme technique.