Glucose turnover rates have been measured in conscious, chronically catheterized, non-pregnant and pregnant rabbits. Non-pregnant rabbits were studied weekly for 4 wk. Pregnant animals were studied once while non-pregnant and then weekly for up to 4 wk during pregnancy. Glucose turnover rate was measured using a primed-constant infusion of [U-14C]glucose and [6-3H]glucose. The weight of the rabbits did not vary throughout the 4-5 wk of study in either the non-pregnant or pregnant group. Seven pregnant rabbits delivered pups which weighed an average of 61 g each. In non-pregnant rabbits, blood glucose concentration did not vary with time. In the pregnant rabbits, blood glucose concentration fell by the end of gestation to an average value of 74.6 +/- 2.7 mg/dl, significantly less (P less than 0.01) than the glucose concentration in the same animals before pregnancy, 88.2 +/- 2.4 mg/dl. The weight specific glucose turnover rate did not vary with time in either the non-pregnant (4.38 +/- 0.16 mg X min-1 X kg-1) or pregnant rabbits (3.89 +/- 0.29 mg X min-1 X kg-1). Blood glucose clearance did not change over time in the non-pregnant rabbits but did increase in the pregnant rabbits in late pregnancy. Blood glucose clearance was inversely related to the fall in blood glucose concentration.