Two new butyrolactone I derivatives: 3-[3-hydroxy-4-(3-methyl-but-2-enyl)-phenyl]-5-(−4-hydroxybenzyl)-4-methyl-dihydrofuran-2(3H)-one (1) and (Z)-3-[3-hydroxy-4-(3-methyl-but-2-enyl)-phenyl]-5-(−4-hydroxybenzylidene)-4-methyl-dihydrofuran-2(3H)-one (2), in addition to the previously described (S)-methyl-4-hydroxy-2-[4-hydroxy-3-(3-methyl-but-2-enyl)-benzyl]-3-(4-hydroxy-phenyl)-5-oxo-2,5-dihydro-furan-2-carboxylic acid methyl ester (3), were identified from a strain ofAspergillus terreusThom (Trichocomaceae) isolated from desert soil. The antifungal activities of both intra- and extracellular metabolites ofA. terreusgrown on yeast extract sucrose and malt extract media were determined. Only the secondary metabolites ofA. terreusgrown on yeast extract sucrose medium were active againstAspergillus fumigatusRCMB 002008. The antifungal activity ofA. terreuswas attributed to the presence of the compounds (1) and (2), whose minimum inhibitory concentrations (MIC) againstA. fumigatuswere found to be 32.00 and 16.00 μg/mL respectively. Structure elucidation was carried out using UV spectrometry, electrospray ionization mass spectrometry (ESIMS), high resolution electron impact (HREIMS) spectrometry, 1H- and 13 C-NMR, proton–proton correlation spectroscopy (1H–1H Cosy), distortionless enhancement by polarization transfer (DEPT), heteronuclear single quantum coherence (HSQC) and heteronuclear multiple bond correlations (HMBC) spectroscopy. Copyright © 2012 John Wiley & Sons, Ltd.