Diterpenoids with trichomonicidal activity were isolated from the aerial parts of Azorella yareta Hauman. One was 13 beta -hydroxy-azorellane, together with the known constituents mulinolic acid, mulin-11,13-dien-20-oic acid, azorellanol and 13 alpha -hydroxyazorellane. Their structures were determined by spectroscopic and chemical methods. (C) 2001 Elsevier Science Ltd. All rights reserved.