Growth curves of bacteria in platelet concentrates were studied to determine whether increasing the shelf-life of platelets from 3 to 7 days might have contributed to the increased number of deaths caused by contaminated platelets that have been reported to the FDA since 1980. Platelets inoculated with 10(3) organisms or more showed logarithmic bacterial growth throughout the 7 days of storage or until the platelets became visibly abnormal. With an inoculum of 10(2) organisms or less, proliferation patterns were variable: 20 percent (%) showed uninhibited logarithmic growth and 50 percent (%) remained sterile throughout the 7 days. In another 30 percent (%), bacterial growth was temporarily suppressed for 5 to 6 days before bacteria actively proliferated. These data support the hypothesis that bacterial contamination of platelets not clinically significant at 3 days of storage might become so during the current 7 day shelf life.