An evaluation of the age distribution of erythrocytes in twin gestation was performed. Based on previous studies on age distribution of erythrocytes in late pregnancy, we have proposed that a more pronounced shift in age distribution of erythrocytes in twin pregnancy may be expected. We have used the density distribution of cells method for evaluation of age distribution of erythrocytes in women with twin pregnancies. Control curves for pregnant and nonpregnant women were obtained from our recently published studies. The cumulative density distribution of cells curve of erythrocytes of women with twin gestation was evidently shifted to the right as compared with the curve of erythrocytes of women with single gestation. The shift in age distribution of erythrocytes may suggest that erythrocytes in women with twin gestation have a shorter life span as compared to the life span of erythrocytes in women with singles. The age distribution shift of erythrocytes in women with twin gestation may be attributed to human placental lactogen augmentation of erythropoietin action.