SUMMARYIn accordance with the biochemical conditions of collagen metabolism in progressive scleroderma and an account of previous experimental investigations of different therapeutic agents in the connective tissue, of animals, we. studied the pathogenetic treatment of this disease with gestagens and give, a detailed report of our own experimental research, in animals and the experience, obtained in patients. Evidence has been presented that an increase of the urinary excretion of hydroxyproline in patients with, progressive, scleroderma is an essential effect of the. progesterone therapy.