Phenolic resoles can be regarded as copolymers of phenol and formaldehyde that are distributed in the chain length and the number of methylol groups per molecule. While other spectroscopic methods like FTIR and NMR only give average structures, MALDI-TOF mass spectrometry is able to resolve the oligomer distribution of phenolic resoles. Using 2,5-dihydroxybenzoic acid or 2,4,6-trihydroxyacetophenone as matrices MALDI-TOF spectra are obtained where each oligomer beak can be assigned to a particular chemical structure. Thus, the degree of polymerization and the number of reactive methylol groups can be determined. For urea-modified resoles, in addition to phenol-formaldehyde and urea-formaldehyde structures, for the first time, phenol-urea-formaldehyde cocondensate structures can be identified directly. (C) 2003 Wiley Periodicals, Inc.