A study of urine alanine-aminopeptidase (AAP), gamma- glutamyltranspeptidase (GGT), and N-acetyl-beta-D-glucosaminidase (NAG) activity and their relation to urine cadmium (7440439) concentrations was conducted. The cohort consisted of 40 male primary smelter workers who were occupationally exposed to cadmium. The comparisons consisted of 36 male hospital workers with no known cadmium exposure. Blood and urine samples were collected. The blood samples were analyzed for cadmium and lead (7439921). The urine samples were analyzed for cadmium, creatinine, NAG, AAP, and GGT. The cohort subjects had urine cadmium concentrations above or equal to 2.0 micrograms per liter (microg/l), mean 10.16microg/l. The comparisons had urine cadmium concentrations below 2.0microg/l, mean 1.00microg/l. The mean blood cadmium concentrations in the cohort and comparisons were 10.22 and 2.08microg/l, respectively. Blood lead concentrations were in the normal range, generally ranging from 100 to 250microg/l. The mean blood lead concentration in the cohort was 134.8microg/l and in the comparisons 9.73microg/l. The difference was significant. Urine NAG and AAP activities, corrected for creatinine, were significantly higher in the cohort than in the comparisons and were significantly correlated with the urine cadmium concentrations. A poorer correlation was seen between NAG and AAP and blood cadmium. GGT activity was not correlated with either urine or blood cadmium. Blood lead did not correlate with NAG, AAP, or GGT activity. Probit analysis showed that significant elevations of NAG and AAP activity occurred at cadmium concentrations below 10 micrograms per gram creatinine (microg/g), the upper limit recommended by the World Health Organization (WHO). The authors suggest that since elevated NAG and AAP activities in cadmium exposed workers may reflect chronic renal tubular nephrotoxicity, urine cadmium concentrations below 10microg/g may cause subclinical tubular dysfunction. The WHO standard of 10microg/g should be regarded with caution.