Treatment with bromocriptine, 30-55 mg daily, in 13 acromegalics for 1-15 months, resulted in a 60% decrease in growth hormone secretion, as judged from the excretion of growth hormone in 24-h urine. Normal excretion was obtained in 10 patients, while 1 patient showed no response. The plasma growth hormone response to O-GTT was improved, but not normalized, in 4 of 7 patients treated for more than 6 months, and marked glucosuria disappeared in two diabetics. While the secretion of TSH, LH and FSH was unchanged, the prolactin secretion was inhibited. The urine excretion of free cortisol showed a 30% decrease, possibly due to a direct effect of bromocriptine on the ACTH-secretion. Hypercalcaemia was never seen, but the initial hypercalcuria showed a modest decrease without measurable changes in the creatinine clearance. The subjective relief during long-term treatment was marked in 10 of 11 patients and the dominating symptoms disappeared in 40-67%, whereas heal-pad thickness, enlarged sellae, and visual fields remained unchanged. No serious side effects were observed. Treatment with bromocriptine seems effective and should be considered as a remedy amongst others, in suitable cases of acromegaly.