Silicotic patients were administered predonisolon-chloroquine diphosphate, tetrahydroxyquinone (THQ) daily for eleven months and their subjective symptoms, heart lung-capacity, chest x-ray, and side effects were observed. Patients given predonisolone-chloroquine diphosphate improved whereas the controls did not. Of the group administered predonisolone-chloroquine diphosphate, twenty-five per cent of patients had improvement of subjective symptoms. All patients had increased maximum breathing capacity, and forty-three per cent had reduction of massive shadow on chest x-ray. In the control group or THQ-treated group, no improvement was found. The side effects of these medicine were gastric troubles (nausea and anorexia) and slight pigmentation of the skin, but no changes were found in blood pictures, liver or adrenal functions. (Thorn's test). From these facts we concluded that predonisolone-chloroquine diphosphate had beneficial effects on the patients but THQ did not.