Substances related to temocillin and products formed by degradation of it in acid and alkali were chromatographed to investigate the specificity of the method. The related substances examined and their retention times are given in this paper. Degradation studies were carried out on solutions containing about 5 mg ml-1 of temocillin in 0.1 M sodium hydroxide solution and 0.1M hydrochloric acid at about 22 oC. After various times aliquots of the solutions were neutralised, diluted 1 + 9 with 0.1 M phosphate buffer (pH 7.0) and injected. In alkali, degradation was complete within 1 h, as shown by the absence of peaks at the temocillin retention times.