The prevention of Rh isoimmunization by the giving of anti‐D gammaglobulin to non‐immunized Rh‐negative women after the birth of an Rh‐positive child is discussed under the following headings: Introduction and the ideas leading to the therapy; Clinical trials; Failures and “failures”. Obstetrical factors relevant to immunization; Risks of the prophylaxis, (a) to the mothers, (b) to volunteer blood donors; Dosage of anti‐D gammaglobulin; The Kleihauer test; Priorities in the use of anti‐D, (a) in abortions, (b) in ABO incompatibility between mother and foetus, (c) in hypertensive patients; Provision of anti‐D gammaglobulin; Mechanisms of protection; Leukocyte antibodies and Rh; The role of intensive plasmapheresis to lo