Administration of intravenous amphotericin B is a major factor in the reduction of the recovery of transfused platelet concentrates (PCs). For the study of possible drug-induced platelet lesions, fresh platelets and stored PCs were incubated with therapeutic concentrations of amphotericin B (10-50 micrograms/mL) and examined for membrane changes by scanning electron microscopy. Stored platelets demonstrated the formation of "pits" on the surface membrane, which were maximal immediately after preparation and gradually decreased with storage. The number of pits was significantly higher after exposure to amphotericin B. No increase was detected in fresh platelets following exposure to amphotericin B. The maximal effect of the drug was seen after 5 days of storage as PCs. Amphotericin B did not affect platelet shape or the number of pseudopodia. There was no correlation between pit formation and the pH, pO2, or pCO2 of the concentrates. Amphotericin B did not release 51Cr from prelabeled stored platelets after 2 hours' incubation at 37 degrees C. Thus, amphotericin B appears to exacerbate a membrane lesion induced by the preparation and storage of PCs.