Bromocriptine (CB-154, Sandoz) has been given to 21 acromegalic patients (11 female, 10 male) for a period of 6-10 months. The mean serum growth-hormone (G.H.) levels ranged from 10 mug/1 to 512 mug/1 before therapy. Bromocriptine suppressed G.H. values to 5 mug/1 or less in 4 patients and to less than 10 mug/1 in a further 8 patients, but in 2 patients G.H. levels did not show any significant reduction. Bromocriptine did not block stress-induced G.H. secretion. It did not distrub pituitary function other than secretion of prolactin and had negligible side-effects. Its effect on tumour size is uncertain and it is therefore unsuitable for patients with suprasellar extension of the tumour. Otherwise it seems reasonable to offer a trial of bromocriptine to all patients with acromegaly where therapy is deemed necessary. In those who show a full response of G.H. levels with a dose of 20-40 mg of bromocriptine per day, external radiation to the pituitary can be used to prevent tumour expansion and bromocriptine withdrawn at intervals to assess the effect of the radiation. In patients with a partial response to bromocriptine, the decision to offer alternative therapy depends on the extent of the response and on the age and medical condition of the patient. In patients who fail to respond to bromocriptine, particularly those younger patients with active disease, more definitive local treatment (e.g., trans-sphenoidal removal of the tumour or yttrium-90 implantation) would be indicated. Bromocriptine may also be used with benefit in the large number of patients who have shown a partial response to other forms of therapy.