The renal function of workers occupationally exposed to cadmium (n = 148), to mercury vapor (n = 63) or to inorganic lead (n = 25) has been compared with that of workers with no occupational exposure to heavy metals (n = 88). A moderate exposure to lead (Pb-B < 62 microgram/100 ml) does not seem to alter renal function. Excessive exposure to cadmium increases the urinary excretion of both low- and high-molecular-weight proteins and of tubular enzymes. These changes are mainly observed in workers excreting more than 10 microgram Cd/g creatinine or with Cd-B above 1 microgram Cd/100 ml whole blood. Occupational exposure to mercury vapor induces glomerular dysfunction as evidenced by an increased urinary excretion of high-molecular-weight proteins and a slightly increased prevalence of higher beta 2-microglobulin concentration in plasma without concomitant change in urinary beta 2-microglobulin concentration. beta-galactosidase activity in blood and in urine is also increased. The likelihood of these findings is greater in workers with Hg-B and Hg-U exceeding 3 microgram/100 ml whole blood and 50 microgram/g creatinine, respectively. The hypothesis is put forward that the glomerular dysfunction induced by cadmium and mercury might result from an autoimmune mechanism.