A high-performance liquid chromatographic (HPLC) method for the simultaneous determination of pralidoxime chloride (I) and its major decomposition products in an injectable formulation is described. I and its decomposition products were detected and quantitated by their UV absorbances at 270 nm, after being separated from related compounds and formulation excipients on a reverse-phase C-18 column using a mobile phase consisting of 52% acetonitrile and 48% of an aqueous solution containing 0.005 M phosphoric acid and 0.001 M tetraethylammonium chloride. The major decomposition products of I in the injectable formulation were identified by their retention times and stop-flow spectroscopy as 2-carboxy-N-methylpyridinium chloride, N-methyl-2-pyridone, 2-carbamoyl-N-methylpyridinium chloride, 2-hydroxymethyl-N-methylpyridinium chloride, and 2-cyano-N-methylpyridinium chloride. A substance of unknown identity also was detected in degraded solutions of I. Stop-flow spectroscopy, employing the spectral discrimination technique, showed that the method is specific for I. Recovery of I from a spiked placebo formulation averaged 99.9%. The accuracy of the method was also demonstrated for the decomposition products over a range of concentrations representing 1-50% decomposition. Replicate determinations of I in degraded solutions gave coefficients of variation of 1.0 and 1.5%, while the precision of determining the decomposition products range from 1.3 to 6.5%. Regression lines with correlation coefficients greater than 0.9999 were obtained for I and its decomposition products, and solutions of these compounds were shown to be stable in the mobile phase for several days. Results for I by the HPLC and USP procedures are compared.