Our recent studies's2 on the constituents of the tropical plant Leonotis nepetaefolia R. Br (Labiatae) have resulted in the isolation and structural elucidation of a number of new labdane ditkrpenes of which nepetaefolin (I) is the most abundant. This comunication reports the isolation of an additional but biogenetically interesting labdane diterpene, methoxynepetaefolin (II), as a minor constituent of L. nepetaefolia. 26 Methoxynepetaefolin has the molecular formula C23H3208 (Mt 436.1985), mp 275-278O, {a)D -35.8' (C 1.2, CHC13), v CHC13 max 1737 (OAc), 1725 (s-lactone) and 1031 cm-l (OMe). The n.m.r. spectrum (1ZDc13)~ of methoxynepetaefolin revealed a close structural similarity to that of nepetaefolin. Thus, two sharp 3H singlets at 1.16 and 2.02 are attributed to methyl and acetate groups at C4 and C6 respectively; absorption due to the methine proton at C6 appeared as overlapping triplets centred at 5.20. Three AB quartets were discernible: the first of these, at 2.30 and 2.62 (J = 3.5 Hz), is due to the protons of the terminal epoxide at C8; the second, at 3.53 and 3.78 (J = 8 Hz), represents absorption due to the methylene protons on Cl6; the third, at 4.00 and 5.10 (J = 11 Hz), is indicative of the methylene protons on C20 which form part of the d-lactone system. A pair of doublets at 4.96 and 5.02 (J = 6 and 3 Hz) are attributed to the X part of an ABX system, these absorptions are therefore ascribed to the proton on C15. Absorption due to the methoxyl group appeared as a sharp singlet at 3.38. No structurally diagnostic features of any significance could be obtained from the mass spectrum4 of methoxynepetaefolin; the main peaks present were at m/e 405 (M-OCH3), 376 (Y-CH3C02H) and 361 (M-CH3C02H -CH3).