IN reviewing the data from 208 cases of erythroblastosis fetalis treated by exchange transfusion, we were surprised to note that although the mortality was over 15 per cent in the whole group, there were no deaths in a group of 42 babies who happened to receive blood from female donors exclusively. This prompted the examination by statistical methods of available data in this large series, which showed that this finding has true significance.It should first be noted that the sex of the blood donor was included in our data only as an afterthought, our interest being turned in this . . .