Melamine-urea-form aldehyde resins are very important commercially, yet little is known about their structures, and the techniques that have been available to examine this are quite limited. In this manuscript we describe the use of H-1-N-15 HMQC NMR spectroscopy and the development of a doubly-selective H-1-N-15-C-13 CP INEPT NMR experiment, to establish for the first time that melamine and urea copolymerize with formaldehyde and to identify the H-1, N-15 and C-13 chemical shifts of the bridging units. This methodology makes it possible to examine co-condensation in industrial preparations of melamine-urea-formaldehyde resins, in order to correlate structure and function and optimize the manufacturing process. (c) 2005 Elsevier Ltd. All rights reserved.