The network structures formed when the diglycidyl ether of bisphenol A is cured with two stoichiometries of diaminodiphenyl sulfone have been studied by solid-state C-13 n.m.r. at temperatures well above the glass transition temperature. High-resolution spectra have been obtained giving detailed information on the chemistry of these structures. Spectral editing and two-dimensional techniques more usually associated with solution-state n.m.r. have been used to confirm structural elements previously postulated. The value of high-temperature n.m.r. for amorphous and rigid systems such as epoxies is discussed.