Data are presented showing that platelets in polyvinyl chloride blood bags plasticized with tri(2-ethylhexyl) trimellitate can be stored on flatbed agitators (shakers) without the pH falling below 6.0. The lowest pH seen after 7 days of storage in 46 units with platelet yields ranging from 3.6 to 13.3 X 10(10) per unit was 6.43. These bags have a O2 transmission rate of 13.3 mumol per hour per bag. Platelet bags with a O2 transmission rate of 7.9 mumol per hour per bag experience a pH fall after 5 days of storage on the shaker in units whose platelet yield on average exceeds 10 X 10(10). Platelets can be stored on first-generation shakers (70 cycles/min, stroke = 1 inch) without an attempt at manual resuspension of the platelet button. The count after 30 minutes on the shaker averaged 89 +/- 15 percent of the expected count, indicating that resuspension was nearly complete after a relatively short period. Red cells, but not platelets, settled out during storage on the shaker.