The crosslinking under pressure of a mixture of novolak with melamine resin has been investigated by means of several techniques, including differential scanning calorimetry, thermal gravimetric analysis, X-ray diffraction, and infrared spectroscopy. The crosslinking of the mixture essentially follows two steps. The former occurs at 150 degrees C and leads to resin networks composed of di- and trisubstituted phenols without significant reaction with melamine polymers. The latter, at 200 degrees C, mainly involves the direct crosslinking of melamine polymers with disubstituted phenols. High pressure, applied to the reaction cell, slows down the crosslinking extent, by inhibiting the formation of trisubstituted phenols. This is probably due to the formation of gaseous by-products of crosslinking. Moreover, a certain structuring effect due to high pressure was observed by means of X-ray diffraction. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 4059-4065, 2009