To the Editor:— In the communication on the treatment of erythroblastosis fetalis inThe Journal, April 28, Dr. Ruth Renter Darrow emphasized certain aspects of the condition which have been neglected. It is conceivable that, in cases in which an Rh negative donor cannot be found, Rh positive blood, given slowly and under constant observation to an erythroblastotic child, may be the lesser evil as compared to no transfusion. So far as these cases go, her statement that no infant should die while Rh negative blood donors are being sought may be a useful antidote to excessive and inflexible dogmatism on the need for Rh negative donors. However, situations in which the use of Rh positive blood is justified would seem to be exceedingly rare. In view of the existence of much misapprehension about the mechanism of erythroblastosis due to Rh incompatibility, it is perhaps more necessary at present to