Heptafluorobutyryl isobutyl ester derivatives of amino acids were determined, using the thermionic nitrogen-phosphorus detector. The linearity of the detector (more than 5 decades), allows determinations above 0.3 pMol and 110 nMol, without the need for further dilution. Due to the specificity of the detector, no fractionation or other pretreatment of the samples prior to hydrolysis were necessary. The separation of the amino acid derivatives ranges from fair to excellent when comparing separations on packed columns with those on capillary columns. On the capillary analyser, however, only a few runs could be performed, since it was not available for a long enough period of time. The reproducibility of the determination was high in the monobasic amino acids, with a coefficient of variation (c.v.) of less than 3, but somewhat worse in arginine, histidine, cystine and minor components. Histidine needs an on-column acylation by the co-injection of the hydrolysate with acetic anhydride. The amino acids tryptophan, cysteic acid and methionine sulphone have not been investigated until now. A disadvantage of the procedure compared with other analytical methods is the rather complicated derivatisation, which until now, has not been easily automated. Finally, the practicability of the method is demonstrated by the results of eightfold determinations in 13 heat-treated (canned) food samples.