Transfusion reactions caused by blood contaminated with bacteria introduced at the time of collection have long been recognized. Such contamination represents a potential hazard with all blood products, but the likelihood is greatly increased when the contributions of several donors are pooled. The article by Buchholz et al. in this issue of the Journal reports a surprisingly high frequency of contamination in platelet pools and clearly documents yet another blood-product vehicle of transmission of clinically important infections. In addition to infections resulting from external contamination of blood products, the unwitting transmission of serum hepatitis, malaria, cytomegalovirus and other infections directly . . .