The chemical composition of the scent gland secretion of Pachylus paessleri Roewer 1913, a pachyline harvestman, was analysed by gas chromatography–mass spectrometry. The secretion is a six-component mixture of benzoquinones, with 2,3-dimethyl-1,4-benzoquinone and 2,3,5-trimethyl-1,4-benzoquinone being the main components (together amounting for ¾ of the secretion). Minor components are 2,5-dimethyl-1,4-benzoquinone (about 12%), 2-ethyl-3-methyl-1,4-benzoquinone (about 8%), 2,5-dimethyl-3-ethyl-1,4-benzoquinone (5%), and 2-ethyl-5-methyl-1,4-benzoquinone (about 1%). No sex-dependent differences could be detected. While dimethyl- and trimethyl-benzoquinones are widespread in scent gland secretions of Gonyleptoidea, 2,5-dimethyl-3-ethyl-1,4-benzoquinone and 2-ethyl-5-methyl-1,4-benzoquinone are reported for the first time in Opiliones. The phylogenetic implications of these compounds are briefly discussed in the scope of the present knowledge of Laniatores.