The preparation of an industrially used sequential formulation of a melamine-urea-formaldehyde resin was followed by matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry and C-13-NMR analysis. The analysis allowed us to identify and follow the appearance, increase, decrease, and disappearance of a multitude of chemical species during the preparation of both the initial urea-formaldehyde (UF) phase of the reaction and the subsequent reaction of melamine with the UF resin that formed. The analysis indicated that (1) the increase and decrease in the species that formed proceeded through a cycle of the formation and degradation of species occurring continuously through what appeared to be a series of complex equilibria, (2) even at the end of the reaction a predominant proportion of methylene ether bridges was still present, (3) some small proportion of methylene bridges already had formed in the UF reaction phase of the resin even under rather alkaline conditions, and (4) the addition of melamine to the UF prepolymer induced some noticeable rearrangement of methylene ether bridges to methylene bridges. (C) 2007 Wiley Periodicals, Inc.