In the studies of mercury concentration both in the air and urine of the workers, and of environments and physical examinations of the workers in a certain factory manufacturing agricultural mercury insecticide, the authors obtained the following results: 1. The mercury concentration in the air of the factory was 0.099~0.225 mg/㎥ , surpassing the maximum allowable concentration. 2. The mercury content in urine of workers ranged from zero to 1,176 γ/l with an average of 370.9 γ/l, showing no fixed relationship with clinical symptoms. 3. Among the workers examined, two showed toxic stomatitis, and three were suspec ted of toxic gingivitis.