A series of carboxylic acid esters are examined by a new technique: drift tube chemical ionization mass spectrometry. Using water as the chemical ionization reagent gas, there Is very little fragmentation of most esters at low values of E/P in the drift tube. At higher E/P, the extent of formation of analytically useful fragments is greater than can be obtained by increasing temperature or switching to methane reagent gas. As E/P is Increased, the onset of each fragment is correlated with the endothermicity of the reaction which forms it. The absence of M+ and (M -1)+ ions In water chemical ionization mass spectra increases the usefulness of the technique for assessing sample purity while the ability to induce extensive fragmentation with the drift tube enables one to obtain structural information from the same sample.