High-quality natural-abundance N-15 cross-polarization/magic-angle spinning (c.p.-m.a.s.) spectra of urea-formaldehyde (UF) resins were obtained by employing a large-volume (2.5 cm3) magic-angle spinning (m.a.s.) rotor. N-15 c.p.-m.a.s. nuclear magnetic resonance (n.m.r.) spectroscopy can clearly distinguish dimethylene ether linkages from methylol groups for UF resins prepared under neutral or basic conditions, a weak point in C-13 c.p.-m.a.s. strategies because of N-14 broadening effects, and can detect the existence of tertiary amides and unreacted primary amides in UF resins. N-15 c.p.-m.a.s. n.m.r. also establishes the fact that there are methylol aggregates that are spatially separated from some other structural moieties in UF resins and that the domain size of methylol aggregates diminishes with the concentration of methylol groups in UF resins. N-15 c.p.-m.a.s. results also indicate that the formation of dimethylene ether linkages is least favourable at pH 9 and most favourable at pH 12 among the three pH values 7, 9 and 12.