Mice were given an intrauterine injection of a carrier solution containing 2 μCi of 1-l4C-glycerol and 10 μCi of D-53 glucose. The mice were killed from zero to five hours after isotope injection and the reproductive tracts and livers were removed and subsequently oxidized to CO2 and H20. Both 14C-glycerol and 3H-glucose were rapidly depleted (P < 0,01) in mice reproductive tracts; 97 % of the 14C-glycerol and 96% of the 3H-glucose disappeared from the reproductive tracts 30 minutes after injection. Fifty-eight per cent of the 14C and 20% of the 3H could be accounted for in the liver in this time. There was a considerable reduction in the activities of 14C and 3H in the reproductive tracts and livers over the remaining 4½ hour sampling period. However, this reduction was negligible in comparison with the initial decrease in activity. Less 14C-glycerol and 3H-glucose disappeared from the reproductive tract at oestrus than at other phases of the oestrus cycle (P<0,05).