Five cases of severe hydrops and erythroblastosis fetalis in association with a large amount of Hb “Bart’s,” all of Chinese origin, are described. The following characteristic clinical and hematologic symptoms were found. There were generalized hydrops, ascites and gross enlargement of the liver. The spleen, however, was not ahvays enlarged. The placenta was large and friable. Severe erythroblastosis of the blood was always found, with reticulocytosis, many target cells and thin cells. The MCV of the red cells was very high. The cells showed an interesting sickling phenomenon. No evidence of isoimmunization was found. In eight parents examined, no abnormal hemoglobin was detected, and alkali-resistant hemoglobin and hemoglobin A2 were not found to be increased. Their blood showed microcytosis of the red cells cxcept in one father and one mother. In this mother, however, the blood was examimied after a blood transfusion. It is thought probable that these were cases of homozygous alpha-chain thalassemia.