Concern over increased bacterial contamination prompted us to conduct a retrospective review of all bacterial cultures performed on cellular blood components at our institution between December 1989 and June 1993. Sterility checks were accomplished by using the Bactec blood culture system. The breakdown of the units cultured versus units produced was as follows: Packed Red Blood Cells (PRBCs): 626 (0.6 percent)/102,593; Random Donor Platelets (RDPs): 523 (0.6 percent)/95,005; and Single Donor Platelets (SDPs): 97 (0.7 percent)/13,641. The units were divided into groups with the following results (cultured/positive): (I) PRBCs implicated in transfusion reactions (159/5); (II) PRBCs issued and returned to lab after 30 minutes (155/0); (III) PRBCs expired on shelf (276/3); (IV) PRBCs used for quality control (QC) (36/0); (V) RDPs implicated in transfusion reactions (309/12); (VI) RDPs used for QC (214/3)); (VII) SDPs involved in transfusion reactions 43/2); and (VIII) SDPs used for QC (54/0). Identification of isolates yielded: Group I = 4 coagulase negative Staphylococcus (CNS) and 1 Enterobacter agglomerans; Group III = 2 gram negative bacilli and 1 CNS; Group V = 12 CNS; Group VI = 2 CNS and 1 Pseudomonas paucimobilis: Group VII = 1 gram variable bacilli and 1 Enterococcus species. Overall, 1.3 percent of all PRBCs, 2.9 percent of all RDPs, and 2.1 percent of all SDPs cultured were positive for bacterial contamination. Although these percentages are low, given the increased susceptibility of immunosuppressed cancer patients, more intensive monitoring of bacterial contamination must be implemented to identify the source of infection.