An ether soluble resin was prepared by extraction and partition of the latex of Euphorbia royleana. This resin demonstrated pronounced pro-inflammatory activity on mammalian skin and was separated into biologically active and inactive fractions by dry column chromatography. The inactive fraction was further separated by adsorption and partition thin-layer methods. The least polar zone consisted of an inseparable mixture of four tetra-esters of the macrocyclic diterpene ingol, whilst the more polar fraction consisted of a mixture of four tri-esters of the same diterpene. A new sesquiterpene lactone, vestolide, of the guaiane series was isolated from the aerial parts of Vicoa vestita. Its structure was established on the basis of chemical and spectral evidence.