Although dust control in West German coal mines has been improved, cases with first x-ray film changes of the lungs were more frequent in 1967 than in 1966. Technical prophylaxis, therefore, has to be completed by a medical one. Its aim is improving lung clearance impaired by quartz-containing mine dust. Medical therapy is needed as well. It is directed against the progression of fibrosis and has to reduce the morphological and functional changes. Injured lung clearance and progressive fibrosis both are due to the cytotoxic action of quartz. Silica cytotoxicity can be prevented by polyvinylpyridine-N-oxide (PVNO). This synthetic polymer renders possible causal prophylaxis and therapy of experimental silicosis. A dose-response relationship and optimum doses of PVNO were established in albino rats. The values are transfered to human conditions. Therapy with PVNO of severe cases of silicosis has begun.