Newly prepared platelet concentrates (PC) and platelet poor plasma (PPP) stored at either room temperature (RT) or 4 C were analyzed for ammonia content initially, and after storage at 24, 48, and 72 hours. These studies demonstrate that ammonia rapidly accumulates in PC stored at RT. This accumulation appears to be temperature dependent, as evidenced by the observed differences in ammonia accumulation in PC stored at 4 C and RT. Whether ammonia acts as a toxic metabolite in the inhibition of platelet function and the development of the "storage lesion," which occurs in PC stored at RT, needs further clarification. Additional studies are also necessary to establish the clinical efficacy of transfusing ammonia-containing platelet concentrates into premature neonates with immature functioning livers, and perhaps into adults with severe liver disease.