Liver dysfunction was produced in the rat by injecting CCl4 subcutaneously in the back twice a week, and the effects of L-carnosine (CAR) on the resulting liver injury were examined. When CCl4 was administered to 6-week-old rats for 9 weeks, GOT and GPT values increased, but these changes were suppressed in the group concomitantly treated with CAR, indicating a protective effect of the agent on liver function. No such preventive effects of CAR was observed in 40-week-old rats, but when the CCl4 administration was discontinued after 4 weeks, GOT and GPT decreased to normal levels within 1 week of discontinuation, indicating a therapeutic effect of CAR on hepatopathy. Based on these findings, we determined the cortisone beta-reductase activity in the rat liver. The increase in this enzyme activity in the group treated with CAR indicated acceleration of cortisone metabolism. Changes of blood cortisol level and cerebral and blood noradrenaline (NA) levels were studied by exposing 6-week-old rats to electric shocks at 30 V. Cortisol released into the circulation after the stress was quickly metabolized in the CAR group and the blood level normalized after 3 hours. Following the release of NA from the brain into the circulation, the NA concentration rapidly returned to the normal level both in the brain and the blood. CAR enhanced the liver function and accelerated the metabolism of stress-related substances also in aged animals. CAR, moreover, restored the RNA contents of the mouse spleen and the immunological abilities represented by PFC reaction, which are reduced by stresses such as forced immersion, fasting, and administration of MMC.(ABSTRACT TRUNCATED AT 250 WORDS)