One of the earliest devices available for plateletpheresis is the Haemonetics system; this machine has been updated recently to permit the use of software in a closed system and thus storage of the collected platelets beyond 24 hours. The authors examined the in vitro and in vivo function of platelets collected on the Haemonetics AutoSurge machine and stored for 5 days in two separate 1000-mL CLX bags. The average count per bag was 1.8 +/- 0.4 x 10(11) in approximately 200 mL of plasma. Immediately following collection, the platelet response to ADP and epinephrine represented 78 and 35 percent, respectively, of the preapheresis values. Aggregation to single stimuli subsequently decreased to 29 and 0 percent, respectively by Day 5. This response is equal to or better than the response reported with the Fenwal CS-3000, the only other plateletpheresis device routinely used for long-term storage. The pH of the preparations was well maintained throughout storage, and there was little alteration in hypotonic shock response or serotonin uptake. Serotonin release decreased consistently. The morphology scores indicated good maintenance of shape immediately following collection; this subsequently decreased after 5 days of storage. Bacterial cultures were negative in all instances. The 51Cr in vivo survival and recovery was good with 65.5 +/- 7.1 percent recovery and an average survival of 7.3 +/- 1.3 days (multiple hit; n = 5). The data indicate that storage of the Haemonetics plateletpheresis product is feasible and that the product is as good as others currently available.