When oestrone is incubated with ox adrenal glands, a number of metabolites are formed which include 6α-hydroxyoestrone (Knuppen, Behm, & Breuer, 1964), 7α-hydroxyoestrone (Knuppen, Haupt & Breuer, 1964), 11β-hydroxyoestrone (Knuppen & Breuer, 1962), 15α-hydroxyoestrone (Knuppen & Breuer, 1964) and 16α-hydroxyoestrone (Knuppen & Breuer, 1962). Among the products isolated, 15α-hydroxyoestrone gave the highest yield. This finding, as well as the recent isolation of 15α-hydroxyoestrone from human pregnancy urine (Knuppen, Haupt & Breuer, 1965), suggested the possibility that 15α-hydroxylation might also occur in the human adrenal cortex. Therefore, the metabolism of oestrone and oestradiol-17β was studied in normal and abnormal human adrenal tissue. These experiments provided also the opportunity of investigating the possible formation of 18-hydroxy-oestrone, a compound which was first isolated by Marrian and his colleagues from human pregnancy urine (Loke, Watson & Marrian, 1957; Loke, Marrian, Johnson, Meyer & Cameron, 1958; Loke, Marrian & Watson, 1959); its synthesis in