Stimulation of human peripheral blood mononuclear cells (PBMC) by pokeweed mitogen bound to erythrocytes (E-PWM) has been found to result in an increased blast cell formation, lymphocyte proliferation, and enhanced immunoglobulin production, compared to stimulation of PBMC by PWM. Using flow cytometric analysis we compared the T helper/inducer (CD4+) to T suppressor/cytotoxic (CD8+) cell ratios of PBMC after stimulation by PWM and by E-PWM. E-PWM was found to induce significantly lower CD4+:CD8+ ratios on days 6 and 9 of the culture than PWM did. This effect was due predominantly to a relative increase in CD8+ T cells after stimulation of PBMC by E-PWM, compared with stimulation by PWM. However, the increase in T suppressor/cytotoxic cells on days 6 and 9 after E-PWM stimulation was accompanied by a simultaneous relative decrease in CD4+/2H4+ T cells (T suppressor-inducer cells) and by a relative decrease in CD8+/Leu-15+ T cells (CD4+/2H4+ independent T suppressor cells) on day 9, compared with stimulation by PWM. These results suggest that the greater immunoglobulin production after stimulation of PBMC by E-PWM than by PWM may be the result of a relative lack of suppression on fully differentiated B cells.