An additive solution has been developed for storage of platelet concentrates (PC) which sustains improved in vivo and in vitro viability after 7 d of storage in second generation oxygen permeable containers. This platelet additive solution is a protein-free physiologic salt solution fortified with citrate, bicarbonate and glucose. The in vivo quality of the PC was evaluated by autologous radiolabelling with Indium-111-oxine to measure recovery and survival by multiple hit analysis. The in vitro quality was evaluated by total ATP content, hypotonic shock response and extent of shape change with ADP. Ten paired studies were performed with PC from the same donor being stored for 7 d at 22 degrees C in both CPDA-1 plasma and the additive solution. Mean recoveries and survivals were found to be substantially higher with PC stored in the additive solution than with PC stored in CPDA-1 plasma (51.0 +/- 7.8% and 144.1 +/- 15.9 h versus 36.6 +/- 10.7% and 110.4 +/- 31.6 h). The differences were statistically significant (P less than 0.001). The results of the in vitro assays described above parallelled the in vivo results, with statistically significantly superior results (P less than 0.01) for all parameters of PC stored in the additive solution. This study is the first to show that PC quality may be improved and storage extended using an additive solution.