1.Thin-layer chromatography of porphyrin methyl esters provides a useful and rapid technique for resolving mixtures of porphyrins from biological samples.2. Application of this technique to urinary, faecal and hepatic porphyrins from patients with symptomatic porphyria revealed five porphyrins of interest which could be identified by mass spectrometry as the methyl esters of porphyrins with 8-, 7-, 6-, 5-and 4-carboxyl groups. Millimolar extinction coefficients at the Soret absorption maxima for these porphyrin methyl esters in chloroform solution were measured.3. A consistent pattern of urinary porphyrin excretion in symptomatic porphyria was seen with 8-, 7-, 6-, 5-and 4-carboxyl porphyrins constituting approximately 60%, 25%, 3%, 3% and 9% of the total respectively. Uroporphyrin (73%), heptacarboxylic porphyrin (26%) and hexa-carboxylic porphyrin (I %) were the only porphyrins detected in the liver of one patient.4. Isomer analysis of excreted and hepatic porphyrins revealed that uroporphyrin was approximately 35% isomer I11 , hepta-and hexa-carboxylic porphyrins almost all isomer I11 and penta-carboxylic and coproporphyrin approximately 50% isomer 111. 5. To explain these findings it is suggested that there are two metabolic pathways for the handling of 6-aminolaevulic acid (ALA) in the liver.Symptomatic porphyria (porphyria cutanea tarda) is a well defined syndrome characterized clinically by increased mechanical fragility, blistering, pigmentation and superficial ulceration of the sun-exposed skin. A history of alcohol abuse and evidence of chronic parenchymatous liver disease can usually be elicited. The serum iron concentration is frequently raised and siderosis of the liver of varying degree is invariably present. Unlike inherited forms of hepatic porphyria, a positive family history of the disorder is exceptional and acute attacks are unknown.The disease is distinguished biochemically by a characteristic pattern of haem precursor

1.The specific activities of urinary uroporphyrin and coproporphyrin were measured as functions of time following the administration of a single oral dose of [4-'"C] b-aminolaevulic acid (ALA) to six patients with symptomatic porphyria and one control subject.2. The peak specific activity of coproporphyrin preceded that of uroporphyrin in all subjects studied and exceeded that of uroporphyrin in the patients with symptomatic porphyria.3. These results are interpreted as indicating the existence of two distinct metabolic pathways in the liver for the disposal of ALA, rather than as contradicting the generally accepted role of uroporphyrinogen as a precursor of coproporphyrinogen.It is generally accepted that the synthesis of haem from glycine and succinate proceeds by a series of ordered biochemical reactions in which d-aminolaevulic acid (ALA), porphobilinogen (PBG), uroporphyrinogen (Urogen), coproporphyrinogen (Coprogen) and protoporphyrin are intermediates. The biochemical steps involved (Fig.