Amino acids are quantitatively determined by precolumn derivatization with 1-fluoro-2,4-dinitrophenyl-5-L-alanine amide and reversed-phase high-performance liquid chromatography with photometric detection at 340 nm. Excellent chromatographic resolution of a mixture of the derivatives of 20 amino acids including proline and cystine is achieved within 110 min by linear gradient elution with acetonitrile in 13 mM trifluoroacetate plus 4% (by vol) tetrahydrofuran. The limit of detection is 50 pmol. Amino acid analyses of acid hydrolysates of the several proteins gave results equivalent to those obtained by conventional ion-exchange-based amino acid analysis. The simplicity of the procedure allows its use on any multipurpose high-performance liquid chromatographic system.