Suppression of the severity of Rh immunization, once it has developed, is difficult if not impossible. Although plasmapheresis may reduce the Rh antibody level somewhat, it is very costly and time-consuming for the results achieved. The Rh hapten is of no value, nor is the administration of Rh immune globulin, once Rh immunization has developed. Promethazine hydrochloride may he of a limited value but may produce some risks to the fetus. Prevention of Rh immunization before it develops, by the administration of Rh immune globulin is much more effective. Prevention is probably always possible, provided Rh immune globulin is given prior to immunization and in sufficient dose. For Rh prevention to suppress Rh immunization to its lowest possible level (2-4/10,000 pregnancies), Rh immune globulin must be given to all Rh-negative, unimmunized women who 1) deliver Rh-positive babies, 2) who abort, or 3) undergo amniocentesis (unless the husband is known to be Rh-negative). The dosage should be at least 300 μg for every 30 ml of fetal blood in the maternal circulation (if Kleihauer examinations arc being done) at 28 weeks' gestation (in Manitoba at least). No Rh IgG should be given to the Rh-negative infant born of an Rh-positive mother. In the future, a sephadex column prepared Rh IgG for intravenous use may be more economical and less likely to produce severe allergic reactions, a rare complication of the intramuscular Cohn cold ethanol Rh immune globulin in use at present.