Abstract Urodiolenone, a compound isolated from the urine of hypertensive subjects, is a 1:1 epimeric mixture of two dihydroxy derivatives of nookatone, a constituent of grapefruit. The structure of urodiolenone was suggested by NMR spectroscopy and confirmed by partial synthesisfromnootkatone, a sesquiterpenoid ketone with a valencene skeleton. In addition, we show that urodiolenone itself is also