In an 8-year study of 18,378 consecutive obstetric patients, irregular antibodies were detected in 299 (1.62%). The incidence of anti-Rha(D) sensitization was 1.66%. The most commonly encountered irregular anti-bodies were: anti-rh´ (C), anti-rh (E), anti-Kell, anti-Lebanti-Lea, and “unidentified.” No neonatal death could be attributed to an irregular antibody alone. Most of the serious problems occurred with the irregular antibody in combination with anti-Rha(D). Routine screening of all Rh-positive and all Rh-negative patients is advisable to provide optimum obstetric care. A cord antiglobulin (Coombs') test must be done oh all patients to alert the clinician to the possibility of erythroblastosis fetalis and the blood bank to rare antibodies, obviating problems if the patient should require a blood transfusion.