Platelet concentrates (PCs), prepared by plateletpheresis, were stored in aliquots in polyvinylchloride blood bags for 5 days at 22 degrees C under rapid, slow, or no agitation. Nonagitated PCs were also stored in a 98-percent oxygen atmosphere. In nonagitated PCs, pO2, lactate production, and platelet factor 4 (PF 4) concentration increased, whereas the ATP level and pH dropped rapidly. These changes were somewhat minimized in nonagitated PCs stored in oxygen. There was no significant difference between the two agitated groups. The increase in PF 4 correlated inversely to the decrease in ATP: r = -0.91, p less than 0.001, n = 24. The formation of thromboxane B2 (TxB2) after stimulation with arachidonic acid or collagen was significantly higher in slowly agitated PCs on Day 5 than on Day 0 (p less than 0.01). Nonagitated PCs produced lower levels of TxB2 (collagen stimulation) on Day 5 (p less than 0.05). In unstimulated PCs, the levels of TxB2 and ATP were inversely correlated on Day 5 (r = -0.70, p less than 0.001, n = 20). In vivo survival was performed after 72 hours of storage; mean survival (+/- SD) was 6.5 (+/- 0.3) days for nonagitated oxygenated PCs and 6.8 (+/- 0.7) days for agitated PCs. In nonagitated PCs, anaerobic metabolism increased, although oxygen diffusion through the container wall was sufficient. Agitation seems to facilitate the diffusion of oxygen through the storage medium. Nonagitated PCs were stored safely for 24 hours; this period can be extended to at least 72 hours when aerobic metabolism is maintained.