Nephrotoxic chemicals are commonly present in the environment, particularly in the workplace. The level of occupational exposure to these chemicals has been so reduced that exposure to these agents now rarely causes clinically evident acute renal disease. A sensitive indicator of renal injury, urinary excretion of N-acetyl-beta-glucosaminidase, was utilized to evaluate persons exposed in the workplace to lead, mercury, or organic solvents, for evidence of renal effects from this exposure. None of the persons had clinically evident renal disease by history, none had hypertension, and all had normal findings on urinalysis. When compared with appropriate control populations, workers exposed to lead, workers exposed to mercury, and two of three groups of workers exposed to organic solvents had significant increases in urinary acetyl glucosaminidase activity. The third group of laboratory workers with low exposure to organic solvents had no increase in urinary acetyl glucosaminidase activity. It is concluded that exposure to environmental nephrotoxins at levels currently considered safe can produce renal effects as manifested by elevations of urinary acetyl glucosaminidase excretion. It is speculated that these renal effects are not always innocuous.