Model samples containing soy, casein, or fish protein were analyzed by gas chromatography and mass spectrometry. The headspace of samples, unheated and heated and with or without fat and starch added, was investigated. Over 150 compounds were identified representing aliphatic hydrocarbons, alcohols, aldehydes, ketones and furan derivatives, and sulfur-containing compounds. The absolute concentrations in the headspace gas were determined for about 80 compounds judged to be of at least potential interest from the aroma point of view. On heating, the concentrations of volatiles generally increase and new compounds are detected. Of particular importance for the aroma of all heated samples is the presence of branched chain aldehydes and sulfur compounds. Moreover, straight chain aldehydes and furans are important in the soy protein samples and hydrogen sulfide in the fish protein sample.