1. Urinary 17-oxosteroid conjugates were measured by gas-liquid chromatography in five patients with hereditary coproporphyria.
2. Three patients were in an acute attack and showed significantly increased excretion of sulphate or glucuronide conjugates of aetiocholanolone. There was increased excretion of several other related steroids but no consistent pattern was apparent.
3. In the two patients in remission, excretion of urinary 17-oxosteroids was not increased.
4. The ratio of total urinary aetiocholanolone to androsterone (5β:5α) was found to be significantly elevated for the three patients in an acute attack. Serial measurements were made in two of these patients and showed a highly significant linear correlation between this ratio and the urinary content of δ-aminolaevulic acid and porphobilinogen.
5. These observations suggest the involvement of the 17-oxosteroids, especially aetiocholanolone, in the pathogenesis of hereditary coproporphyria.