Bacterial contamination of platelets poses the greatest risk of mortality and morbidity to platelet transfusion recipients. Some European countries have introduced routine bacterial monitoring of platelets to reduce the risk of transmission of bacteria. A pilot study was carried out at the Northern Ireland Blood Transfusion Service, using the BacT/ALERT automated culture system, to assess the operational feasibility of routine bacterial monitoring of platelets. About 4885 platelet concentrates (PCs) were tested in a 1-year period. Of the 28 (0.57%) initial reactive cultures, 13 (46%) were reproducible on repeat culturing. Of these, 10 were detected within 24 h of incubation either in aerobic or both aerobic and anaerobic culture bottles. A sample of time-expired units (423) that had initial negative culture results remained negative when retested on day 8. About 213 time-expired units were subjected to routine quality assessment and more than 85% were found to conform to quality standards specified in the UKBTS guidelines for platelet count (> or =240 x 10(9) per adult dose PC) and pH (6.4-7.4). There was a reduction in the platelet count because of the volume removed (15 mL) for sampling. Routine bacterial testing with day 2 sampling and a negative culture result after 24 h as a mandatory release criterion would improve product safety. Implementation of 100% testing would be operationally feasible but may require extension of the shelf life if unacceptable wastage is to be avoided.