1. The fate of mevalonate, the product of HMGCoA reductase, was studied in male and female frogs (Rana esculenta) in order to explain the circannual variations of enzyme activity. 2. The incorporation of 2-14C MVA into unsaponifiable lipids, cholesterol and dolichol in liver, plasma and eggs was followed. 3. Labeled MVA shows a different utilization depending on season and sex. In spring and summer cholesterol synthesis is related to hepatic reserve storage in both sexes, while the peak of enzyme activity, present only in females in fall, seems committed to cholesterol export into the blood and uptake by the oocytes. 4. The presence of a MVA-derived protein identifiable with vitellogenin and labeled on the lipid moiety, suggests that HMGCoA reductase activity in fall is committed to the lipidation of this protein essential for oocyte maturation.
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