The 9.5 GHz electron spin resonance (e.s.r.) spectra of single crystal and powder samples of y-irradiated A taurine, H,NCH,CH,SO,-, have been recorded. Overlapping spectra from three distinct radicals are present. The first of these is the species SO,-with an isotropic g-value of 2.0035 and a 33S hyperfine coupling tensor with principal values 135.2, 99.2, and 97.9 G. The second radical is a n-electron species with the unpaired electron mainly on carbon and exhibiting hyperfine interaction from at least four protons, probably +