As part of a continuing study of adrenal steroids in relation to breast cancer, various experiments were performed in order to study relationships between androgen and corticosteroid biosynthesis. Chopped tumour tissue from a 'mixed cell' adrenal adenoma (7·4 g.) removed from a patient in Cardiff Royal Infirmary was incubated with [4-14C]pregnenolone and [7α3H]17α-hydroxypregnenolone for periods of time ranging from 30 to 120 min. The results of this work suggest that 17α-hydroxyprogesterone may not be an obligatory intermediate in androgen or cortisol synthesis. Evidence from further experiments with 'normal' human adrenal tissue removed from breast cancer patients using previously established ultramicrochemical techniques indicates that dehydroepiandrosterone (DHA) sulphokinase enzyme system is confined to the zona reticularis of the gland. The conversion of [7α-3H]DHA sulphate, [7α-3H]androstenedione and [7α-3H]testosterone to oestrogens and their conjugates by adrenal homogenates was also investigated. Conversions were extremely low from all precursors.