Using population genetics it was demonstrated that two newly discovered blood factors of chimpanzee blood, Acand Bc, and the blood factor Nvdetected byVicia graminealectin, belong to the same blood group system, designated the V‐A‐B blood group system. In a study of 60 chimpanzees, all eight of the theoretically possible phenotypes were encountered. By gene frequency analysis, it was demonstrated that five of the eight possible genes postulated by the genetic theory of multiple allelic genes occurred among these 60 animals. A suitable nomenclature has been formulated which incorporates the facts observed.In the analysis of the findings, a paradox was encountered in the application of the 2 × 2 contingency test. This paradox has been resolved and expla