The frequencies of antigen‐incompatible matings within the HLA, Rhesus, Lutheran, MN, S. Lewis, Kell, P and Duffy systems were studied in 481 parents of karyotyped spontaneous abortuses. The results were compared with the calculated mating frequencies in control samples consisting of 1,197 (HLA) and 12,123 (the remaining eight systems) individuals, respectively. The only significant difference observed at the 5 % level was an increased frequency of matings in which the mother was Lu (a +) and had a karyo‐typically abnormal abortus. It is concluded that antigen incompatibility between the parents within the nine systems studied is not important in the aetiology of early spontaneous abortion or causative in the origin of chromosome anomalies in the foetus.