Exposure of dilute solutions of m-dinitrobenzene or s-trinitrobenzene in methyltetrahydrofuran to 60Co γ-rays at 77 K gave two species detectable by e.s.r. spectroscopy. One, favoured at low doses, had features characteristic of monoanions with the unpaired electrons primarily localised on one nitro-group. Similar anions were formed from the nitro-derivatives in methanol (CD3OD). At high γ-ray doses a second species grew in at the expense of the monoanions. These had half-field (ΔMs± 2) transitions characteristic of triplet states, and well defined features in the parallel regions of the anisotropic ΔMs± 1 transitions. These parallel features, which exhibited no resolved hyperfine coupling to 14N were used to estimate average effective separations between the two unpaired electrons, giving values in the region of 5–6 Å. The ΔMs± 1 perpendicular features were poorly defined but gave clear evidence of 14N hyperfine coupling. The (14N) parallel features were better resolved in the ΔMs± 2 transitions, which showed five shoulders indicating two equivalent nitrogen nuclei with about half the coupling of the monoanions. These results are all in accord with the postulate that the species involved are dianions in triplet states. Each unpaired electron must be strongly localised on one nitro-group which cannot be twisted far from the limit of coplanarity. Absence of 14N coupling on the ΔMs± 1 parallel features can then be understood since the 14N parallel axes are perpendicular to the principal axis for the zero-field coupling. The alternative explanation for these results, that solvent radicals are trapped close to the radical anions is considered, but ruled out on the grounds that the ΔMs± 2 features should then be triplets rather than quintets, and because there would be no barrier to chemical reactions between such radicals and the nitrobenzene anions.