The in vitro response of lymphocytes to dsDNA, Sm, and Pokeweed Mitogen (PWM) and the role of monocytes in the control of this response were studied in 21 SLE and 14 healthy individuals. Specific hemolytic plaque assays were used to enumerate peripheral blood B lymphocytes secreting anti-dsDNA and anti-Sm antibodies. After 7 days in tissue culture without stimulation, anti-dsDNA or anti-Sm Plaque Forming Cells (PFC) were observed in 75% of SLE patients and 45% of normals. PWM, dsDNA, and Sm stimulation raised the levels of anti-dsDNA PFC in 25%, 37%, and 83% of SLE cultures respectively, and in all but one normal culture. PWM and dsDNA induced a decrease in anti-dsDNA PFC in 50% and 62% of SLE cultures. This suppressive effect was mainly exerted on spontaneous high producers of anti-dsDNA PFC. Monocyte depletion from cultures resulted in a decrease in PFC formation in all normals studied and in 7 SLE cultures. In 2 SLE cultures with no stimulation and one dsDNA stimulated culture, the number of anti-nuclear PFC increased after monocyte depletion. In cocultures of allogeneic, HLA-DR identical mononuclear cells, dsDNA pulsed SLE monocytes appeared more efficient than pulsed normal monocytes in helping to generate anti-dsDNA PFC. SLE lymphocytes responded less well than normals to dsDNA. These results suggest that: nuclear antigens may act as stimulators or suppressor of the specific autoimmune response, depending on the immune status of the SLE patient; and that abnormalities in both monocyte and lymphocyte responses lead to the excessive secretion of anti-dsDNA and anti-Sm antibodies by SLE B lymphocytes.