Blood samples for bacteriological study were obtained from 101 obstetrical patients immediately after delivery of the placenta, and again on the morning of the first postpartum day, in order to observe the frequency of bacteremia during labor. Four of the samples at the end of labor yielded bacterial growth, one organism being a coagulase-positive staphylococcus. Eleven of the samples obtained next day yielded growth, one organism being an alpha-hemolytic streptococcus. Thus, only two potentially pathogenic organisms were found, but the hazard of bacteremia in connection with labor was seen to be real. Patients believed to be susceptible to recurrent subacute bacterial endocarditis appear to need the same protection during parturition as is needed by similar patients during dental extractions, tonsillectomies, and urologic procedures. Prophylaxis with antibiotics is therefore justified in such cases.