N-15 variable contact time (VCT) cross polarization magic angle spinning (CPMAS) NMR experiments were employed to investigate the reaction products formed in wood composites bonded with N-15-enriched polymeric diphenylmethane diisocyanate (PMDI)-based adhesives. Two wood species were studied. Aspen (Populus tremuloides) and Southern Pine (Pinus sylvestris). The influence of temperature and wood moisture content on the distribution of PMDI-derived species are presented and discussed.