Collagen content and mutual relationship between type I and type III collagens in the skin of rats chronically treated with some antiinflammatory drugs were evaluated. It was found that prednisone, colchicine, acetylsalicylic acid, indomethacin and phenylbutazone induce a decrease of collagen content in rat skin. In the case of prednisone, acetylsalicylic acid and phenylbutazone modification of type I to type III collagen ratio in rat skin was observed. These observations suggest that non-steroid antiinflammatory drugs may exert similar effects on skin collagen as steroid hormones.