Eighty patients with advanced metastatic renal cancer have been treated with hormones, chiefly medroxyprogesterone acetate (Provera). This progestational compound is remarkably free from side-effects and can be given in high dosage for long periods without serious complications. Ninety per cent of cases had multiple metastases: in 76% more than one organ was involved and nearly 50% were seriously ill or "terminal".Subjective improvement occurred in at least 55%. In 11 patients there was marked improvement in the radiological or clinical signs of tumour within 2 to 6 weeks of commencing treatment or changing to a different hormone. In two further cases improved general health was associated with stationary metastases for 20 months. A significant objective response occurred in 16% of the total series. A favourable response was seen more often in men (21%) than in women (8%). If deaths within 6 weeks are excluded the objective response rate in men is increased to 27%. Although the response of advanced renal cancer to hormonal treatment is usually incomplete and of brief duration, it is possible for such treatment to offer a "new lease of life" to a seriously ill patient, even in old age, for 2 to 3 years.