The extent of the renal contribution to postabsorptive endogenous glucose production (EGP) in humans is controversial. We measured EGP in the absence of the liver during the anhepatic phase (AH) of liver transplantation in five patients (aged 46.4+/-10.2 years, two women). Stable labeling of plasma glucose (PG) was achieved for a 2-h period before the AH by primed continuous infusion of di-deuterated 6,6[2H2]glucose (1.7 mg/min) and continued throughout the AH. PG was maintained above the fasting level (6.1+/-2.73 mmol/l) with 5% dextrose labeled with 6,6[2H2]glucose throughout the AH (mean level during the AH 0.98+/-0.45 mg x kg(-1) x min(-1)). Isotopic enrichment remained stable at 0.84+/-0.21% atom percent excess throughout. EGP, calculated by use of a modified Steele equation, decreased from 2.6+/-1.24 at baseline to 0.97+/-0.9 mg x kg(-1) x min(-1) (36% baseline, P = 0.045) but recovered at approximately 30 min to reach 1.38+/-0.83 mg x kg(-1) x min(-1) (54% baseline) by 60 min. Epinephrine, lactate, free fatty acid, and glycerol levels increased significantly (0.79+/-0.74 to 3.65+/-2.1 nmol/l, P = 0.005; 1.88+/-0.43 to 3.46+/-0.9 mmol/l, P = 0.024; 543.9+/-215.5 to 705.5+/-219.2 micromol/l, P = 0.012; 75.6+/-30.2 to 139+/-96.3 micromol/l, P = 0.003, respectively). These data show that postabsorptive nonhepatic glucose production in humans may contribute to greater than one-third of overall EGP, increasing when required, and that it is associated with a stress response and increased gluconeogenic substrate availability. We conclude that extrahepatic tissues, most notably those of the kidney, make a significant contribution to EGP in humans.