The metabolism of glucose has been studied in 48-h-old unanesthetized fasting and post-absorptive sucking piglets. Both [6-3H]- and [U-14C]glucose were administered either by a single injection method or by a primed infusion technique. The rates of glucose turnover and recycling were estimated under steady-state conditions. The rates of glucose turnover and recycling in 48-h-old fasting or post-absorptive piglets were not statistically different when measured using the single injection technique or the primed infusion method. The mean (with SE) rate of glucose turnover was 65.8 (2.5) in post-absorptive and 31.1 (1.9) mumol/kg per min in fasted newborn pigs. Glucose utilization was linearly related to blood glucose concentration; regression analysis indicated a y-intercept of 7.2 mumol/kg per min. As tested by arterio-portal differences the gut was not releasing glucose or galactose in 5 h-post-absorptive sucking newborn pigs. Thus, the higher rates of glucose turnover in post-absorptive newborn pigs compared with fasting ones suggest that hepatic glucose production is enhanced in post-absorptive sucking piglets. The mean (with SE) rates of glucose recycling were four times higher in post-absorptive piglets than in fasting ones, i.e. 14.4 (1.6) and 3.7 (0.5)% of [6-3H]glucose turnover respectively. As liver glycogen was exhausted in 48-h-old sucking piglets, this suggests that hepatic glucose production results from gluconeogenesis.