To provide the basic for assessment of renal dysfunction related to silicosis, urinary N-acetyl-beta-D-glucosaminidase(NAG) activity known as a sensitive markers for early renal damage were measured in 58 silicosis patients, and control subjects of 40 pulmonary tuberculosis patients and 51 official workers. The results were summarized as follows. 1. The values of blood urea nitrogen and serum creatinine in all subjects were within reference limits. But the mean value of urinary NAG activity(7.25+/-7.31 U/g creatinine) was beyond reference value and more sensitive test than others. 2. The mean value of urinary NAG activity in silicosis group was 11.98+/-9.05 U/g creatinine and significantly higher than in tuberculosis and healthy group(p<0.01), but the mean values of NAG activity in tuberculosis and healthy group were not different(p>0.05). 3. The value of NAG activity in tuberculosis had a tendency to be increased according to severity of disease, but that was not significant(p>0.05). The value of NAG activity was increased significantly by use of nephrotoxic antituberculosis drugs(p<0.05). 4. The value of NAG activity in silicosis had a tendency to be increased according to the size of nodule, use of nephrotoxic antituberculosis drugs and shortness of onset duration, but the increase was not significant(p>0.05). 5. After excluding the users of nephrotoxic antituberculosis drugs, the mean values of NAG activity in healthy control and in tuberculosis control were same as 3.63 U/g creatinine and 3.60 U/g creatinine, respectively. But the mean value of NAG activity in silicosis group was remarkably increased as 10.90 U/g creatinine(p<0.01). As above results, even though there are no abnormal findings in screening renal function test, silicosis can be related with renal dysfunction. And it will be very useful to apply urinary NAG activity in health management of workers exposed to dust.