The constitutions of the cyclopolyarsines (AsR)n (R = methyl, ethyl, n-propyl, and phenyl) have been investigated by nuclear magnetic resonance and mass spectrometric techniques. A systematic study of their fragmentation under electron impact at different ionization potentials has confirmed the presence of pentameric alkyl and hexameric phenyl cyclic arsines. Variable temperature N.M.R. spectra obtained for pentamethylcyclopentaarsine have been interpreted in terms of a rapid pseudorotation process. Some mixed methylphenyl cyclic arsines have been identified.