The aim of this study was to evaluate the in vitro activation in platelet suspensions collected with CS 3000 Plus and Cobe Spectra cell separators using platelet storage containers and the role of white blood cell (WBC) concentration of the suspension in this activation. Seventy-seven donors were subjected to automated platelet donations with 1 type of equipment (37 with Cobe Spectra and 40 with CS 3000 Plus). Blood samples were obtained immediately after separation and on the third day of storage at 22 degrees C in constant agitation. The WBC concentrations of these samples were studied before storage. Paraformaldehyde-fixed platelets were incubated with 2 murine monoclonal antibodies: CD42b and CD62. Murine monoclonal antibody immunoglobulin G was used as a negative isotypic control. Bound antibody was then quantitated by flow cytometry. On the third day of storage, a significant increase in CD62 expression rate was observed in platelet suspensions collected with both kinds of equipment. Mean expression rates for Cobe Spectra on Day 0 and Day 3 were 25.6 +/- 6.2% and 69.2 +/- 9.7%, respectively. Mean expression rates for CS 3000 Plus on Day 0 and Day 3 were 23.4 +/- 8.2% and 67.0 +/- 8.2%, respectively. The mean results for both devices were 22.8 +/- 4.56% for Day 0 and 68.7 +/- 13.2% for Day 3. There was no difference between CD42b mean fluorescence intensity on Days 0 and 3 for the 2 devices (p > 0.5). Mean WBC concentrations in the platelet suspensions for Cobe Spectra and CS 3000 Plus were 0.37 x 10(3)/microl and 0.42 x 10(3)/microl, respectively, and there was no relation between WBC concentration and increase in CD62 expression. Both kinds of equipment were found to be similar according to in vitro activation markers.