The characteristic absorption spectra of aromatic amino acids between 240 and 310 nm were used to identify tryptophan, tyrosine, and phenylalanine-containing peptides. In acidic solution, the absorption spectra of these amino acids exhibit minima or maxima at 255, 270, and 286 nm. Based on these characteristics, the content of the aromatic amino acid in peptide can be estimated. For this study, 2 nmol of tryptic peptides from human apolipoprotein A-1 was separated by high-performance liquid chromatography using a reverse-phase column. The peptide fragments were monitored by a photodiode-array spectrophotometer. This new approach offers a rapid, simple, sensitive, and direct identification of peptides containing aromatic amino acids. Those containing Trp, which may be of interest for DNA sequencing and important in sequence analysis of proteins, can be selectively purified using this technique.