THE present emergency has provided an unusually abundant opportunity for the study of syncope, or fainting, in blood donors. Although not in itself serious, fainting results in loss of time to the donor, it is detrimental to the efficiency of the donor center, and, as pointed out by Taylor,1 an occasional donor has fallen and suffered injury. The present investigation of some of the clinical and etiologic aspects of syncope was undertaken to aid in reducing the incidence of fainting in blood donors. Aside from practical considerations, it is hoped that the observations and data recorded in this paper will . . .