Information on the masses of the end groups of four poly(styrene) polymers, with relatively low average molecular weights and polydispersities, has been obtained from matrix-assisted laser desorption/ionisation-collision induced dissociation (MALDI-CID) data. The masses of the end groups were calculated, using the equations shown, from the mass-to-charge ratios of two series of intense ion peaks that were observed at low mass-to-charge ratios in the MALDI-CID spectra. Certain mechanisms are proposed here to account for the formation of these ions and others that: are observed in the spectra.