A high-performance liquid chromatographic method is described for the assay of angiotensin-converting enzyme in human serum and for the separation of angiotensins and their analogues after pre-column fluorescence derivatization with benzoin. Angiotensin II, formed enzymatically from angiotensin I, is converted into a fluorescent derivative which is then separated isocratically from the substrate and biological substances in the enzyme reaction mixture on a reversed-phase column (TSK gel ODS-120T). The lower limit of detection for angiotensin II is 0.66 pmol per enzyme assay tube. The method is simple and sensitive, and requires as little as 5 microliter of human serum. Angiotensin analogues can also be separated and quantified by the chromatographic technique, and thus this method permits the use of the analogues of angiotensin I as substrates.