Peripheral blood mononuclear cells (PBMC) were collected as a byproduct of plateletpheresis of normal blood cell donors using modifications to standard automated protocols on either the CS-3000 or Spectra blood cell separator machine. Comparison of the PBMC products obtained showed X +/- SD WBC yields of 5.3 +/- 3.4 vs. 3.8 +/- 2.0 x 10(9) with the CS-3000 and Spectra, respectively (P < .0001). The majority of the cells were lymphocytes, with 13-15% monocytes with both machines. Sixteen percent of the WBC collected with the Spectra, but only 1% of those collected with the CS-3000, were granulocytes. The CS-3000 PBMC product contained fewer RBC (0.2 +/- 0.1 x 10(11) vs. 2.4 +/- 0.6 x 10(11)) and more platelets (1.6 +/- 0.6 x 10(11) vs. 0.35 +/- 0.39 x 10(11)) in a smaller volume (40 +/- 14 ml vs. 229 +/- 37 ml) than the Spectra products. Comparison of the platelet collections harvested when PBMC were also collected to platelets harvested using standard procedures on the same machine showed no change in platelet, WBC, or RBC yields for the Spectra. A significant increase in mean WBC contamination from 40 +/- 56 x 10(7) to 112 +/- 205 x 10(7) and a small, but statistically insignificant, decrease in platelet yield from 4.1 +/- 1.2 x 10(11) to 3.9 +/- 1.8 x 10(11) was observed in the CS-3000 platelet collections when PBMC were harvested. There was no sustained change in donor lymphocyte counts and no change in acute donor side effects or time requirements when PBMC were collected.(ABSTRACT TRUNCATED AT 250 WORDS)