He I and He II photoelectron spectra (UPS) of isomeric mono- and bis(ethynyl)furans were recorded. The assignment of spectra was based on empirical considerations (bandwidths, He II/He I intensity variations, comparison with spectra of related molecules) and ab initio calculations. The details of orbital interactions between the ring and ethynyl st orbitals were deduced solely on the basis of experimental data. These interactions were studied for several classes of it isoelectronic molecules.