The trimethylsilyl derivatives of approximately 50 compounds related in structure to biogenic catecholamines have been studied in terms of their gas chromatographic and mass spectrometric behavior. The electron impact mass spectra of the trimethylsilyl derivatives of 3,4-dihydroxyphenylethylamine, 3,4-dihydroxyphenylacetic acid and 3,4-dihydroxyphenylethylamine and deuterated isotopic variants were compared to determine fragmentation characteristics of the amines, acids, alcohols and amino acids within this class of compounds. Analysis of shifts in the masses of major diagnostic ions in the spectra of structural analogs of these compounds has shown that structural modification of the structure can be identified and localized within these molecules. The gas chromatographic characteristics of these derivatives are reported, in terms of methylene unit values.