Abstract 1. 1. Purine-nucleoside: orthophosphate ribosyltransferase (E.C. 220.127.116.11) activity was found in the hepatopancreas of the land snail, Helix pomatia (Gastropoda) during the active period and in hibernation. 2. 2. With our enzyme preparation inosine was the best substrate followed by guanosine and adenosine, while xanthosine and uridine were not cleaved. 3. 3.The enzyme properties resembled those of the chicken liver enzyme, but no inhibition by ADP and Na 2SO 4 was observed. 4. 4. Ribosyltransferase is postulated to participate in the pathway leading from IMP to xanthine and uric acid—the end-products of protein metabolism in H. pomatia. Phosphoribosyltransferase (E.C. 18.104.22.168) and ribohydrolase (E.C. 22.214.171.124) catabolic activities were not found in the same preparations.