Ion-pair reversed-phase high-performance liquid chromatography together with fluorescence detection is useful in the analysis of urinary porphyrin carboxylic acids. The sensitive and quantitative detection facilitates the clinical diagnosis of porphyrias. The method described permits the detection of porphyrins down to 0.1 ng directly from urine without laborious sample pre-treatment. A linear response curve was obtained from 0.2 up to 200 ng for coproporphyrin I. The within-assay correlation coefficients ranged from 2.5 to 10.1%. Recovery experiments gave an accuracy of 89-109%. The rapidity and simplicity of the method allows its application to the routine analysis of urinary porphyrins in the clinical laboratory.