A simple, precise, and accurate spectrophotometric determination of antazoline salts was developed by improving the ceric sulfate procedure. Replacement of water with acetic acid for the preparation of all assay solutions permitted reproducible measurements of the chromogen that absorbed at 505 nm. An appreciable increase in color stability was attained by the controlled addition of perchloric acid to the ceric reagent prior to interaction with antazoline at room temperature. Evidence is provided to account for the oxidation of antazoline at the expense of a complex ceric species. Other 2-imidazolines or phenylephrine did not interfere with the investigated color reaction. In addition to the high value of the chromogen molar absorptivity, ideal adherence of color absorption to Beer's law permitted accurate and reproducible estimation of antazoline over the 1--10-microgram range. The procedure was applied to the analysis of different antazoline dosage forms.