We evaluated stabilized whole blood control materials for their performance as a routine control material for immunophenotyping using flow cytometry. These materials serve as the method control, controlling for both the binding of monoclonal antibodies to the cells and the efficiency of the red-blood-cell lysing reagent. Three products (FluoroTrol, StatusFlow, and CD-Chex): were tested. The controls performed very well in evaluating both CD4 and CD8 percentages and absolute cell counts using flow cytometry. Light scattering patterns and fluorescence intensity of antibody binding were slightly different from those of normal whole blood. These products are not appropriate for quantitative fluorescence standards. Cytometry (Comm. Clin. Cytometry) 38:268-273, 1999. Published 1999 Wiley-Liss, Inc.