Eleven patients with PRL and three with GH-secreting pituitary adenomas were treated with a single intramuscular injection of 50 mg of bromocriptine retard (Parlodel, LA (long-acting)). There was a marked PRL suppression in 9 prolactinoma patients, in four for a period of at least 6 weeks. In one patient with acromegaly GH plasma levels decreased into the normal range. The size of the pituitary adenoma diminished considerably, as shown by CT scan, in three out of the 9 responding patients with prolactinoma and in the above acromegalic patient. Visual fields normalized within 14 d in one patient with a PRL-secreting macroadenoma and bitemporal hemianopsia who also had CT scan-documented shrinkage of the tumour. There were no side-effects except slight hypotension in two and local tenderness at the injection site in one patient; these symptoms disappeared without treatment. It is concluded that bromocriptine retard is a safe and effective therapeutic tool for shrinking hormonally active pituitary tumours in selected patients. Due to its good tolerance and the rapid hormonal and clinical improvement it may be also considered as the best therapeutic approach to initiate the treatment of PRL- and/or GH-secreting pituitary tumours.