The evaporation-grinding MALDI-TOF MS sample preparation method and evolved gas analysis/GC/MS (EGA/GC/MS) were used to study the cyclodehydration of polybenzoxazole and poly(benzoxazoleamide) precursors. Precursor fibers were heated from 100 to 300 degrees C while evolved gases were monitored by GC/MS; after each heating, samples were removed for MALDI-TOF MS analysis. Changes observed in MALDI-TOF mass spectra result from cyclodehydration, along with end group, and structure modifications (due to decarboxylation and branching). Evolved gas analysis/GC/MS and thermogravimetric analysis data indicate mass loss (from chain rupture) and evolution of low mass material which lead to branching. Cured polybenzoxazole fibers display an overall predominance of branched species with minor reduction in molecular weight whereas cured poly(benzoxazoleamide) fibers yield linear species as the predominant product with only minor branching observed and significant reductions in molecular weight. Results from this study indicate that a combination of MALDI-TOF MS and EGA/GC/MS has great potential for examination of thermal, chemical, and photodegradation pathways of high molecular weight, condensation polymers.