Hamsters infected with Opisthorchis viverrini, a liver fluke of man, showed an increased deposition of collagen in their livers. However, increased collagen breakdown as well as its synthesis were observed in the infected livers. Thus, stimulated synthesis might be the main factor responsible for the net increase in collagen content. Synthesis and degradation increased to a greater extent in short-term infection than in long-term infection whereas the hepatic collagen content was equally elevated in both cases. The results, therefore, suggested a difference in collagen metabolism of short-term and long-term infected livers.