Conventional HPLC analysis of the sesquiterpene aryl esters present in the crude extracts of the pathogenic basidiomycete Armillaria is complicated by difficulties in identification solely on the basis of retention time. On-line coupling of liquid chromatography with thermospray mass spectrometry (LC-TSP-MS) provides a means for their direct detection. Crude extracts of seven Armillaria species were analysed providing a semi-quantitative survey of sesquiterpene aryl ester production within the genus. The distribution of these metabolites and its significance with regard to species differentiation and pathogenicity are discussed. Unknown components were also detected by on-line LC-TSP-MS screening of extracts, facilitating a targeted isolation route.