SUMMARY: A Pettenkofer and sulphuric acid chromogen, excreted as a glucuronide and found in the fractions of urine that also contain hydroxylated Δ5-3β-hydroxysteroids and pregnanediol, was identified as p-menth-1-ene-8,9-diol (uroterpenol). Pettenkofer chromogenicity in a compound of this nature has not previously been reported. The recovery of uroterpenol in urine after ingestion of limonene showed that it was a metabolic product of this unhydroxylated monoterpene. Although experiments on its excretion by normal subjects indicated that it was largely, if not entirely, of dietary origin, there was evidence that its rate of excretion in women was influenced by endocrine factors. Hormonal effects on the formation and/or excretion of glucuronides in general are suggested. Care is needed to ensure that dietary constituents and their metabolites, which are excreted as glucuronides and exhibit colour reactions commonly used in the estimation of urinary steroids, are not confused with hormonal metabolites.