Microbiological contamination of manipulated blood products, including hematopoietic progenitors obtained from peripheral blood, is an infrequent but persistent problem in transplant units. The relevance of such contamination in causing patient infection has been reported as insignificant, but the effect on the post-transplant course has not been well documented. We studied the incidence of bacterial contamination in autologous peripheral blood progenitor cell transplants in two of the bench processing steps, as well as the repercussions in the post-transplant course affecting incidence of infections, transfusion requirements and time to engraftment. A total of 365 aphereses performed on 152 patients were cryopreserved in 617 bags. In 31 of these bags (5.0%), bacterial cultures were positive for Coagulase-negative Staphylococcus (31.1%), S. epidermidis (21.9%), Corynebacterium sp. (6.3%), S. warneri (6.3%), Stenotrophomonas maltophilia (6.3%), Streptococcus sp. (9.4%), Viridans group Streptococcus (3.1%) and more than one bacteria (Coagulase-negative Staphylococcus plus Corynebacterium) (15.6%). Half of the bags were contaminated at the time of freezing and the others at the time of thawing. The 31 contaminated bags were infused into 17 patients. In five of these the same contaminating bacteria was found. No difference between the two groups of patients (contaminated and non-contaminated) was found on the day the fever started, length of fever, blood transfusion requirements and engraftment, but length of hospitalization was significantly greater in patients receiving contaminated transplants.