1.Study has been made of the mass spectra of certain ethers and diethers of the cyclopropane series.2.Under electron impact, the alkoxycyclopropanes (C3H5OR) break down to give C3H5O fragments, while the vinyl- and phenoxycyclopropanes decompose with the formation of regrouped [M-H,-CO]+ions. Mechanism are proposed to cover these processes.3.The fragmentation of the 1-alkoxy-1-phenoxycyclopropanes is largely determined by the presence of the cyclopropane ring in the molecule; study of the decomposition products makes it possible to determine the structure of the parent compound.