Platelet concentrates were prepared using the Haemonetics Model 30 (M-30) and a multiunit bag pheresis method. Comparisons of collection efficiency using paired donor collections and posttransfusion recovery using the same donor-recipient pairs were made for the two methods. The M-30 proved consistently superior as a method of collection in terms of efficiency and yield per hour (p less than .001). When the platelets obtained were transfused to HL-A matched, clinically stable, thrombocytopenic patients with acute leukemia similar increments within the expected range were obtained at 1 hour and 18 hours posttransfusion. While the M-30 is a more efficient collection method, the bag method is still relatively efficient and may be more suitable for smaller centers and specialized uses.