Apheresis procedures that optimize peripheral blood stem cell (PBSC) harvesting also result in a significant loss of platelets to the patient/donor because of their similar densities. We compared the percent drop in platelet count and hemoglobin concentration in the patients before and after PBSC collection using two different collection chambers with the CS-3000. A modified plateletpheresis procedure was utilized. Seven patients underwent 38 PBSC collections during steady state hematopoiesis using the standard A-35 collection chamber. At the end of the procedure, a second low-speed centrifugation of the PBSC concentrate was performed in the manual mode, with siphoning out and return of the PRP to the patient through a transfer pack. For 14 patients who underwent 113 PBSC collections, a small volume collection chamber (SVCC) was substituted for the A-35 chamber and the second centrifugation step was omitted. These patients were also primed with 4 g/m2 of cyclophosphamide. The percent drop in platelet count in the patients after the collection procedures was significantly less in the SVCC group (20.4 +/- 9.1 vs. 36.0 +/- 12.3, P = 0.000), even after correction for the difference in the volume of blood processed between the two groups (3.2 +/- 1.4 vs. 3.9 +/- 1.3, P = 0.006). The percent drop in hemoglobin concentration was also less with the SVCC both before (5.4 +/- 3.8 vs. 11.7 +/- 3.0, P = 0.000) and after (0.8 +/- 0.6 vs. 1.3 +/- 0.3, P = 0.000) correction for the difference in the volume of blood processed.(ABSTRACT TRUNCATED AT 250 WORDS)