Effects of intraportal influsion of glucagon in vehicle concurrent to feeding on meal pattern were studied in rats with reference to the changes of glycogen content in the liver. The feeding of the animal was monitored by an eatometer in the test chamber. The removal of a Noyes peller, 45 mg, in the food trough activated both a food dispensor to deliver another one and an infusion pump to infuse fluid into the hepatoportal vein at a rate of 0.35 ml/min for 30 sec. The infusion pump was on active state 23 hr/day for consecutive 15 days with a sequence: saline from 1st to 5th day, glucagon in saline (3 micrograms/ml) from 6th to 12th day, and again saline from 13th to 15th day. During the experiment, 7 groups of 5 rats in each were sacrificed at different times for determination of the glycogen content of the liver and the glucose level in the hepatic and hepatoportal veins. The data of 10 rats that proceeded up to the 12th day of infusion and those of 5 that continued to complete the whole course of 15 days infusion were used for analysis of meal pattern. The results revealed that the food intake was uniformly depressed during the period of glucagon administration and that the reduced food intake was totally accounted for by the premature termination of meals. The hepatic glycogen was depleted with glucagon initially but tended to come back with time. However, hepatic hyperglycemia was maintained without abating.(ABSTRACT TRUNCATED AT 250 WORDS)