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).