We measured the expression of the IgE Fc receptor, Fc epsilon RII, on peripheral blood monocytes isolated from asthmatic patients and normal subjects by laser flow cytometry. After peripheral blood mononuclear cells were incubated with monoclonal antibodies, H107, which recognize Fc epsilon RII, FITC-labeled second antibodies were reacted with them. The cells were then incubated with PE-labeled Leu M3 monoclonal antibodies and the ratios of H107 positive monocytes were measured by two color analysis. The ratio of H107 positive monocytes in atopic asthmatic patients was significantly greater than the ratio in normal subjects. But the ratio was not higher in 9 out of the 14 atopic asthmatic patients. This indicated that atopic asthmatic patients are divided into two groups by the expression of Fc epsilon RII on monocytes. Total serum IgE level was not related to the ratio of H107 positive monocytes.