Two apheresis systems (COBE Spectra and Fenwal CS-3000 Plus with TNX-6 chamber [CS-3000 Plus]) were compared by using their yield predictors and maximum processing times in regard to platelet yields and processing times (n = 200 each). Platelet yields (n = 50 each) and white cell (WBC) content (n = 20 each) from procedures using the current software revision (3.6) on the Spectra and various interface offset (10) settings on the CS-3000 Plus were also compared. Significantly higher median platelet yields (4.88 [range, 1.84-9.97] vs. 4.57 [range, 2.82-9.20] x 10(11) platelets) and frequency of components with greater-than-or-equal-to 6.0 x 10(11) platelets (31.5 vs. 21.5%) were found with the Spectra. In the study with Spectra and the CS-3000 Plus 10 settings, 10-10 and 10-13, overall, produced the most platelets, although the differences were not significant. All Spectra collections tested had <5 x 10(8) WBCs, and, depending on the software revision, had either 85 percent (revision 3.6) or 100 percent (revision 2.5) of components with <5 x 10(6) WBCs. To ensure that 1 00 percent of components contained <5 x 10(8) WBCs when the CS-3000 Plus was used, 10 settings of 10 or less were required, and to ensure components with <5 x 10(6) WBCs, only 10(-6) could be used. Spectra and CS-3000 Plus were capable of collecting large doses of platelets (up to the equivalent of 18 units) in processing times of 67 to 100 minutes with <5 x 10(6) WBCs.