Thirteen patients with prolactin-secreting and/or growth hormone secreting pituitary tumours have been treated with bromocriptine in doses of about 10 mg/day for several months. Nine of these patients were previously submitted to external or interstitial radiotherapy and one case to pituitary microsurgery. Serum prolactin concentration in patients with prolactinomas was still very high within one year after pituitary irradiation or operation, i.e. 5,125.6 +/- 974 mU/l (mean +/- SEM). It has been reduced to normal level only during bromocriptine therapy, i.e. to 329.1 +/- 88mU/l (p less than 0.001), and increased thereafter, but remained to a significantly lower concentration than before bromocriptine treatment, i.e. 2,709.0 +/- 553 mU/l (p less than 0.05). Serial pneumonecephalotomography has demonstrated the reduction of tumour size afrer bromcriptine therapy to two prolactinomas with suprasellar extension. In patients with acromegaly the effects of bromocriptine were less evident. The antitumoral effects of bromocriptine on prolactin-secreting adenomas is independent and additional to the effects of pituitary radiotherapy or microsurgery, and has therapeuticical implications.