The styrene-crosslinked mixed polyesters derived from maleic anhydride, 2,2-di-(4-hydroxypropoxyphenyl)propane and I,2-propylene glycol were studied by means of high-resolution C-13 n.m.r. in the solid state (CP/MAS). The proton spin-lattice relaxation time, T-1(H) and spin-lattice relaxation time in the rotating frame, T-1 rho(H) were determined and compared with corresponding values calculated for hypothetical mixed ester/styrene copolymers. The results, found to be consistent with T-g data, were interpreted in terms of the mixing, copolymer and crosslinking effects.