BACKGROUND There are conflicting data on the effect of irradiation and subsequent storage on the quality of platelet components. METHODS The retention of platelet properties during storage of gamma-irradiated apheresis suspensions was studied in 22 apheresis components obtained on a cell separator with a specialized centrifugation chamber. Immediately after collection, each suspension was divided equally into two 1-L polyolefin containers. On Day 1 (n = 12) and Day 3 (n = 10) one of each pair of suspension containers was gamma radiated with 2500 cGy. All platelet suspensions were stored for 5 days at 20 to 24 degrees C. Samples were drawn on Day 5 from each of the 22 pairs of containers for evaluation of an array of in vitro properties. Samples were taken from 10 pairs of containers for platelet labeling with either 51Cr or 111In for subsequent transfusion and concurrent in vivo measurement of recovery and survival. Posttransfusion samples were drawn after 24 hours for ex vivo whole blood aggregation. RESULTS Comparable in vitro and in vivo properties were measured in irradiated and control platelets, whether irradiation was performed on Day 1 or Day 3. The mean +/- 1 SD in vivo recovery and survival time for controls and platelets irradiated on Day 1 was 52 +/- 14 percent and 146 +/- 34 hours and 51 +/- 7 percent and 147 +/- 36 hours, respectively. For Day 3 irradiation, the values were 46 +/- 12 percent and 150 +/- 60 hours and 47 +/- 9 percent and 151 +/- 53 hours, respectively. A small, but measurable adverse effect of irradiation on ex vivo platelet aggregation was present. CONCLUSIONS These data indicate that storage of apheresis platelets after gamma radiation is without clinically significant, demonstrably adverse effects on platelet quality.