Pooled platelet concentrates of different platelet count and volume were stored in gas-permeable plastic bags. Adequate oxygen supply kept the glucose consumption and therefore the lactic acid production relatively low. The change of pH seemed to depend largely on the platelet count and on the volume of the concentrate. The in vitro functions showed a decrease together with the adenine nucleotide content. The reduced in vivo viability of stored platelets corresponded to decreased hypotonic stress response, as well as to lowered ATP content. The results suggest that storage of platelets in gas-permeable bags may extend the shelf-life of pooled platelet concentrates, but the actual amount of platelets present should be taken into consideration.