Abstract
A haemagglutination inhibition test, developed specifically for primates, diagnoses early pregnancy in the chimpanzee, gorilla, orang-utan and baboon. The test was sensitive and reacted positively when the concentration of gonadotrophin in urine was equivalent to 0·03 i.u. human chorionic gonadotrophin per ml. This degree of sensitivity and the certitude that it cross-reacts with primate luteinizing hormone probably accounts for most of the false positive results.