We have studied the effects of lead, cadmium and hexavalent chromium in cultured human lymphocytes. Both the proliferative response and the generation of antibodies were evaluated, and the metal accumulation in the cells was measured. Lead added in the range of human exposure caused a significant enhancement in Ig production, which was related to the Pb concentration in the cells. An inhibitory effect on blastogenesis, was detected at Cd doses found in occupationally exposed subjects. Chromium induced reductions in both blastogenesis and Ig production in relation to its capability to enter the cells.