Testing of infants suspected of having necrotizing enterocolitis for evidence of exposure of the Thomsen-Friedenreich cryptantigen (TCA) has been advocated, because patients with TCA exposure can have severe hemolytic reactions when undergoing transfusion with plasma containing blood products. We compared 62 patients who were managed with knowledge of TCA exposure status during a four year period with 66 patients who were not screened during a comparable four year period. Evidence of hemolysis after blood transfusion occurred significantly more frequently in patients who were not screened (42 versus 15 percent, p < 0.05) and there was significantly greater mortality (18.0 versus 4.5 percent, p < 0.05) in the group that was not screened. These findings suggest that screening for TCA exposure is not only of diagnostic and prognostic value in necrotizing enterocolitis, but is important for patient management and outcome.