The effects of plane of nutrition on blood flow in the portal vein (PBF) and on the rate of clearance of progesterone from the circulation (MCR) were measured for 14 or 24 h in six ovariectomized gilts given 1 or 3 kg of food per day. On a body weight basis, PBF was significantly increased by the increase in food intake from a mean for all gilts of 14·9 ml/kg.min (1·34 litres/min) on 1 kg to 21·6 ml·kg. min (1·96 litres/min) on 3 kg, a mean increase of 45 %. Metabolic clearance of progesterone was increased by a similar percentage, 47·1%, from 41·0 ml/kg.min (3·70 litres/min) to 60·3 ml/kg.min (5·67 litres/min) by the increase in food intake. Both MCR and PBF were lowest between 04.00 and 06.00 h, increasing after each feed except that when 3 kg/day was fed the MCR remained high throughout the period between meals. In two gilts, blood flow in both the portal vein and hepatic artery (HAF) was measured. The mean PBF and HAF for each pig were 40·6 and 5·8, and 32·4 and 35 ml/kg, min respectively. HAF was 11·2% of total hepatic blood flow.