Two-color immunofluorescence using multiparameter flow cytometry was employed to examine the antigenic characteristics of peripheral blood lymphocytes in whole blood of healthy Caucasians and Japanese. The CD4/CD8 ratio in Japanese was significantly decreased compared with that in Caucasians, because of the increased number of CD8+ cells. Although the proportions of suppressor-inducer T cells (CD4+, Leu-8+) and helper-inducer T cells (naive T cells) (CD4+, CD45RA-) were low in Japanese subjects, there were no differences in the absolute numbers of suppressor-inducer T cells and helper-inducer T cells (naive T cells) in circulation. The level of activated T cells in Japanese was similar to that in Caucasians. NK cells, CD57+, CD8+ cells and CD57+, CD3+ cells were high in Japanese. Regarding B cell subsets, CD5+ B cells and activated B cells remained unchanged. However, there were slight differences in Leu-8+ B cells and Fc epsilon R+ B cells (CD20+, CD23+) between the two groups. Thus, a differing influence of racial and environmental background between healthy Caucasians and healthy Japanese on human lymphocyte subsets is present in the lymphocyte immunophenotype.