Continuous intraportal infusion of pancreatic glucagon during a feeding test conducted in the dark phase of the circadian photoperiod produced a dose-related suppression of feeding in rats. At the end of the 30 min of infusion, food intake was suppressed 10% at the infusion rate of 0.33 micrograms X kg-1 X min-1 and 45% at the highest infusion rate studied (100 micrograms X kg-1 X min-1). At infusion rates of 33 and 100 micrograms X kg-1 X min-1, the suppression of cumulative intake persisted for 30 min after the termination of the infusion, but no effect on 24-h intake was observed. Glucagon's glycemic effects were measured for two glucagon doses (1 and 10 micrograms X kg-1 X min-1) in the absence of food using a paradigm similar to that used for the feeding tests. In contrast to the suppression of food intake, the hyperglycemic effects of glucagon were not dose related for the two doses tested. The hyperglycemia was similar in magnitude 5 min after the start of the infusion at both infusion rates. Subsequently, plasma glucose concentrations declined more rapidly at the higher than at the lower glucagon dose. This difference in the effect of glucagon on glucose disposal may be important for glucagon's satiating effect.