The Environmental Protection Agency's National Environmental Research Center, Cincinnati, Ohio, undertook a study to explain why phenylmercuric salts such as the chloride, hydroxide, benzoate, acetate and others chromatograph with identical retention times even though they have very dissimilar anionic character. Programmed temperature GC analysis using an FID was used to determine if any products of what was suspected of being a conversion phenomenon were being overlooked using electron capture detectors. Compounds producing peaks were collected using a splitter system and identified using infrared and mass spectral analysis. Results show phenylmercuric salts are converted in the injection block to diphenylmercury as the chief chromatographable product of what may be a free-radical reaction. Phenylmercuric chloride is produced at the same time in a quantity related to the amount of chloride contamination in contact with the sample. The peak commonly associated with each of the salts was found to be phenylmercuric chloride. Because phenylmercuric salts are converted in this unpredictable way, accurate quantitation is very difficult, and differentiation is impossible. One exception is phenylmercuric chloride which, when injected, produces a relatively small, reproducible amount of conversion to diphenylmercury. Therefore, the analysis for phenylmercuric salts should be carried out by converting them to the phenylmercuric chloride to insure results that represent an accurate and precise measure of that particular class of organomercuric mercury extracted from the sample.