The objective of this study was to quantitate the antibody binding capacity (ABC) of CD3, CD4, CD8, CD16, and CD19 on lymphocytes and CD4 on monocytes from healthy adult donors. Peripheral blood was collected over three consecutive days and repeated in the same format two weeks later for comparison to initial measurements. Immune subsets were labeled by direct single or two-color staining in whole blood followed by lysis of erythrocytes. Fluorescence intensity measurements were made by carefully calibrating the flow cytometer and then measuring the intensity of monoclonal antibody staining on labeled cells and on Quantum Simply Cellular Microbeads. The effect of paraformaldehyde fixation on intensity measurements and coefficient of variation of thirty replicates for each phenotype were also studied. We found a small change in calculated ABC following overnight fixation with a greater change following 48 h of fixation prior to flow cytometric analysis. We found excellent precision could be achieved for measuring the ABC of most markers with some improvement desirable for expression of CD4 on monocytes and CD16+ lymphocytes. Between donors we found a high-low range of CD3+ = 134,349-45,905; CD4+ (lymphocytes) = 54,174-36,106; CD4+ (monocytes) = 9,246-3094; CD8+ = 268,868-190,622; CD3+CD8+ = 269,858-212,024; CD16+ = 38,307-336; and CD19+ = 25,252-11,689. For the total donor group, the observations at week 1 and week 2 were not significantly different (alpha = .05) for any of the immunophenotypes we studied. The data presented here continue to show that it is possible to perform quantitative intensity measurements of immune subsets when performing immunophenotyping studies.