Sonchus macrocarpus Boulos et Jeffrey so far has not been investigated chemically. The aerial parts afforded lupeyl acetate and its Δ¹² isomer, β-amyrin and its acetate, lupeol, sitosterol and its glucoside, pinoresinol (1) and two sesquiterpene lactones, molecular formulae C₁₅H₂₀O₄ and C₁₅H₂₂O₄, which could not be separated. The ¹H NMR spectral data (Table 1), especially in deuteriobenzene, showed that the eudesmanolides 2 and 3 were present. The main compound, 2, was obviously a methylene lactone because of the typical lowfield doublets at δ 5.97 and 4.83. Spin decoupling, starting with these two signals, allowed the assignment of all other signals. The presence of an aldehyde group at C-4 could be deduced from the doublet at 9.51 which was slightly shifted in the spectrum of 3. The stereochemistry followed from the couplings observed Though the signals of the minor lactone 3 could be assigned only in part, the most important ones were visible and they allowed the assignment of the structure and the stereochemistry. As J₇,₁₁ was 12 Hz the Me-11 group was α-orientated. Compound 2 we have named sonchucarpolide. The chemistry of the genus Sonchus, which is placed in the tribe Lactuceae in the subtribe Crepidinae [1] or in a separate Sonchus group [2], still does not give any clear indications concerning relationships to other groups. Eudesmanolides are reported from two Sonchus species [3,4], but the guaianolide jacquinelin was also isolated [5]. Several triterpenes and sterols of different types have been reported too [6,7] as well as flavones [8] and some coumarins [8]. However, many more investigations are necessary to get a more distinct picture of the chemotaxonomy of this group and the whole tribe.