Barbatusol, isolated from the labiate Coleus barbatus Bentham, is shown to be a new phenolic diterpene with a rearranged abietane skeleton. Absolute configuration is established by hemisynthesis of barbatusol dimethyl-ether from the known carnosol. Barbatusol is endowed with biological activity. Known as "boldo" in Brazil, the Labiate Coleus barbatus Bentham is largely used in popular medicine against liver fatigue and intestinal disorders. Several abietane diterpenes have been isolated from the leaves of the plant grown in Brazil, whilst the leaves of C. barbatus of Kenya afforded highly unsaturated rearranged abietanes and the roots of the Indian C. forskolii (syn of C. barbatus) furnished polyhydroxylated labdane diterpenes, two of them, forskoline and colenol, exhibiting potent antihypertensive activity. This prompted us to reinvestigate the Brazilian C. barbatus looking for new cardioactive compounds. In this paper, we wish to report on the isolation, structure elucidation, absolute configuration and partial synthesis of barbatusol (I), (5S)-9(10→20)-abeo-abieta-1(10),8,11,13-tetraen-11,12-diol, a new bioactive diterpene obtained from C. barbatus collected in the surroundings of Rio de Janeiro.