The mechanism of the liver damage in acute pancreatitis remains unsolved. The aim of this study was to evaluate RNA and DNA changes in the liver in Na-taurocholate pancreatitis in rats, with consideration being given to the protective effect of prostacyclin (20 micrograms.kg.24 h intraperitoneally). Total RNA increased both in treated and untreated rats after 24 hrs and even more after 48 hrs. After 48 hrs this increase was 35% higher in treated than in untreated rats. The RNA/DNA ratio paralleled the increase of total RNA. In 24 hrs incorporation of 3H-uridine into RNA increased 145% in untreated, and in 48 hrs 50% in treated rats. After 7 days 60% of treated animals survived as compared with 20% in the untreated group. The evident changes in RNA content, RNA/DNA ratio and RNA synthesis suggest a role for nucleic acid disturbances in the liver injury in acute pancreatitis. The beneficial effect of prostacyclin might, in part, be dependent on its effect on nucleic acid metabolism.