Chronic occupational exposure to toluene was studied in a factory preparing tarpaulins. Seventy-eight workers were studied; 46 were exposed to various concentrations of toluene in air (20--200 ppm), 32 were unexposed workers in the same factory. In many cases the exposure had lasted for 10--20 years. The urinary hippuric acid excretion at the end of work shift showed good correlations to toluene concentrations in air, and it seems to be a good measure of exposure. The hippuric acid in urine samples collected overnight showed that elimination of toluene still occurs several hours after exposure. Most of the biological parameters measured showed no correlation to toluene exposure. The blood leukocyte count did not show slight positive correlations to toluene exposure, but even this parameter stayed inside the range of normal values. The occurrence of chronic diseases, drug using habits, and drinking and smoking habits did not show any correlations to toluene exposure.