Due to their poor solubility in organic solvents, triazine-based polyamines are very difficult to characterize with respect to chemical structure and molar mass. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is shown to be a unique method for investigating both the reaction between substituted 2,4-dichloro-s-triazines and diamines, and the chemical structure of the reaction products. Using formic acid as the solvent and 2,5-dihydroxybenzoic acid as the matrix, well-resolved spectra are obtained and oligomer series with different end groups are identified. It is shown that partial hydrolysis of the chlorine groups of the s-triazine which leads to chain termination, may be prevented by changing the catalyst. Investigation of the reaction of a s-triazine with phenylene diamine revealed that in addition to the incorporation of phenylene diamine into the polymer chain, the self-condensation product, 2,7-diaminophenazine is incorporated as an end group. Although quantitative information on the composition of the products cannot be obtained directly at present, the qualitative description of the polycondensation process by MALDI-MS is very valuable for further investigations.