Determinations of hypochlorous acid and chloramine compounds are important in a number of areas. Several techniques are now available for such analyses, but most require unstable reagents and/or multiple steps in the analytical procedure. We have developed a simple, one-step spectrophotometric assay for reactive chlorine-containing compounds involving the oxidation of ascorbic acid by hypochlorous acid or chloramines. There is no interference from other nonhalide oxidants such as hydrogen peroxide or hypothiocyanous acid. Because small amounts of ascorbic acid will not damage biological materials, this method also allows continuous measurements of the generation of chlorine-containing compounds by activated neutrophils. This simple assay permits precise analysis of as little as 1 nmol of HOCl.