The effects on renal functions of infusing glucagon (100 ng kg-1 min-1) into the portal vein system were studied in young anaesthetized sheep kept on a diet with normal protein and digestible energy contents. The clearance measurements of the left kidney functions showed a decreased urine flow rate (from 0·36 ± 0·04 to 0·18 ± 0·03 ml min-1; P < 0·01) within the first 10 min of glucagon infusion, falling to 0·07 ± 0·02 ml min-1 (P < 0·01) during the next 10 min. The glomerular filtration rate also decreased from 17·56 ± 2·92 ml min-1 to its lowest value, 3·34 ± 1·02 ml min-1, (P < 0·01) after 20 min of glucagon infusion. Decreases in urea excretion (from 53·1 ± 6·46 to 3·82 ± 1·27 μmol min-1; P < 0·01) and osmotic clearance (from 0·67 ± 0·13 to 0·09 ± 0·02 ml min-1; P < 0·01) occurred during the first 20 min. The plasma level of glucose increased from 4·01 ± 0·53 to 8·33 ± 1·12 mmol l-1 (P < 0·05) 20 min after the start of glucagon infusion. Twenty minutes after the start of glucagon infusion, the values of all the parameters measured began to recover, although they did not reach the control level, even after 1 h. Blood pressure was stable during the whole experiment. The results show that the effects of intraportally infused glucagon on kidney functions in sheep are the opposite of those obtained from similar experiments in laboratory animals with simple stomachs or in humans.