In vivo 13C-NMR was employed to determine the hepatic fate of infused [1-13C]-d-glucose (200 mg/kg) following ad libitum or routine meal feeding (RMF) regimes imposed during pregnancy. Hepatic glycogen synthesis was measured immediately following the last meal in virgin, 10 and 20 day pregnant rats. No detectable incorporation of 13C-glucose into glycogen was observed in 20 day pregnant and control fed virgin rats. In 20 day pregnant RMF rats, glycogen synthesis from 13C-glucose occurred at a linear rate of 0.10/s (S.D. 0.018/s). By 50 min post-infusion, 13C-glycogen levels were 131% (p<0.01) higher than those seen for the 22 h starved and 2 h refed virgin group. Following 10 days of gestation, glucose incorporation into glycogen was maximal in both the ad libitum and RMF groups. Compared with the 20 day pregnant RMF group, the 10 day pregnant ad libitum and RMF rats produced 146% (p<0.001) and 315% (p<0.001) more incorporation of 13C-glucose into the glycogen macromolecule, respectively. Hepatic glycogen values were similar for both 10 and 20 day pregnant ad libitum rats (65.7±4.7 and 58.8±4.5 mg/g weight) but lower in the RMF groups by 58% and 48%, respectively. In conclusion, meal feeding regimes in the pregnant rat alter carbohydrate control of the liver producing increased glycogen synthesis initially via direct incorporation of glucose into the macromolecule.