OBJECTIVE To investigate the synthesis and degradation of type IV collagen in CCl4-induced SD rat liver fibrosis. METHODS Dynamic changes and relationships among the tissue alpha 1 (IV) procollagen mRNA, type IV collagen (Col IV) and serum 7S polypeptide fragment of Col IV in fibrotic livers induced by CCl4 with choline difficiency diet were studied using immunohistochemistry, Northern analysis, in situ hybridization and serum RIA techniques. RESULTS The transcription of alpha 1 (IV) procollagen mRNA in fibrotic liver and the content of serum 7S polypeptide fragment derived from tissue Col IV degradation was enhanced promptly and obviously in earlier stage of experiment, but not synchronous afterwards. In the early stage of experiment, alpha 1 (IV) procollagen mRNA transcripts was localized in sinusoid Ito cells and endothelial cells. In the mid and late stage, alpha 1 (IV) procollagen mRNA transcripts was localized in myofibroblasts (MFs), fibroblasts (Fbs) and endothelia of small blood vessels in fibrotic septa. CONCLUSIONS The change of serum 7S polypeptide fragment could reflect the motabolic state of Col IV and the degree of tissue injury in fibrogenesis and might have some clinical significance in identifying the activiation of the liver fibrosis. The "Ito cell-myofibroblast-fibroblast" effective cell system and sinusoid endothelia were the Col IV producing cells during fibrogenesis, in which sinusoid endothelia, as another source of Col IV production, participated in the capillization of liver sinusoids.