Blood-typing investigations of whales were undertaken for the first time in the antarctic in 1960-1961. Individual variations in antigenlc specificities were detected in both finback and pygmy-blue whales. The frequency of occurrence of Ju blood types of finbacks suggested that a portion of the Atlantic population from area II migrates to area III and mingles with the population there. Ratios of this intermingling were estimated. Significant differences in the apparent rate of pregnancy by blood-types were the occurrence of isoantibodies. The data strongly suggested the possible occurrence of abortion of fetuses caused by maternal-fetal incompatibility in blood types in both species of whales. This prenatal mortality rate can be assumed to depend upon the frequency of Ju blood types, and this postulate should be kept in mind in subsequent studies.