A soluble monoterpene primary alcohol:NADP⁺ oxidoreductase has been purified to apparent homogeneity from leaves of the catmint, Nepeta racemosa. The purified enzyme consisted of two polypeptides, with molecular masses of 42, 000 and 40, 000 Da, and contained zinc ions. A number of monoterpene alcohols (geraniol, nerol, citronellol, and their hydroxylated derivatives) were substrates, but the enzyme was inactive toward ethanol. The enzyme required NADP(H) as cofactor, with NAD(H) ineffective. Gas chromatographic and coupled mass spectrometric analysis of the reaction products showed that 10-hydroxygeraniol and 10-hydroxynerol were oxidized by the enzyme in the presence of NADP⁺, at both C-1 and C-10. These results are consistent with a role for this enzyme in the biosynthesis of iridoid monoterpenes.