The combination of trilostane 960 mg daily and either dexamethasone 0.5 mg b.d. or hydrocortisone 10 mg b.d. has been used to treat advanced metastatic breast cancer in post-menopausal women. Twenty-three patients had assessable disease and received treatment for a minimum of 8 weeks. Six (26%) showed an objective response and three (13%), stabilisation of previously progressive disease, sustained for at least 3 months. Side-effects were mainly gastrointestinal. Biochemical studies suggest that the mechanism of action may be inhibition of conversion of androstenedione to oestrone.