A wide range of thiols have been exposed to 60Co γ-rays at 77 K both in the pure state and in dilute methanolic or aqueous glasses. Spectra assigned to RS· radicals had gz values (z is along the C–S bond) which varied with the environment, but which were all close to 2.158 in methanol. Dissociative electron capture at sulphur (RSH + e–→ R·+ SH–) was only observed in methanolic or aqueous glasses, and it is postulated that solvation of the ejected SH– ion plays an important role. The structure of a species (X) containing two sulphur atoms and having g values close to 2.058, 2.025, and 2.001 is discussed. Two rival structures, RS·–SR2 and RSS· are considered in depth and it is concluded that the former is most probable unless both species have very similar properties. Electron loss to give RSH+ followed by reaction to give R(H)S·–S(H)R+ cations is postulated to explain certain features in the e.s.r. spectra, as an alternative to proton loss to give RS· radicals.