Flow cytometric lymphocyte gating methodology influences B-cell counts. B-cell counts were calculated from peripheral blood using flow cytometric immunophenotyping in 18 patients with a clonal B-cell population of CLL phenotype, using 3 methods of lymphocyte gating and comparing with a quantitative bead-based methodology as the standard. All patients had an ALC greater than 5.0 × 109/L (range, 5.2-19.6 × 109/L). Variation in B-cell count was observed depending on the gating method used. Arrows indicate 7 of 18 patients had B-cell counts greater than 5.0 × 109/L using one method, but less than 5.0 × 109/L using one of the other methodologies.