A total of 2391 serum specimens from pregnant women were tested for antibodies to red cell antigens. The results of the study demonstrated that allosensitized subjects account for 2.6% of the examinees. Most frequently, the allosensitization of mothers was caused by anti-D antibodies (monospecific or combined with antibodies anti-C and anti-E), which were detected in 48 women. 14 women had alloantibodies of other specificity: anti-E, anti-cE, anti-c, anti-C, anti-C-w. anti-Le(a), anti-Kp(a), and anti-Lu-a. Of 47 newborn babies, whose mothers had alloantibodies, 18 babies were healthy; 27 had hemolytic disease of newborn (HDN), and 2 fetuses died of edema. Severe HDN was observed if mother had antibodies anti-D and antic. Antibodies of the anti-E, anti-C and anti-C-w specificity caused mild HDN, whereas antibodies anti-Le(a), anti-Kp(a) and anti-Lu-a,3 did not cause HDN.