Eight patients with macroprolactinomas were treated with a long-acting injectable form of bromocriptine, depot-bromocriptine (Parlodel LAR). With the exception of one male patient who had partial and short-lasting suppression of PRL levels after two injections and who underwent a second adenomectomy, the patients were given Parlodel LAR injections at 28-day intervals for six months. In all patients, there was a significant fall in serum PRL levels after the first injection. PRL secretion was suppressed to within the normal range in 3 of 7 patients on long-term treatment. PRL was consistently within the normal range in 2 patients from the sixth week and in one, from the 14th week onwards. In the other 4 of 7 patients, a marked suppression of PRL secretion, resumption of menses, and normal libido and potency were recorded. In 3 of 8 patients, no adverse effects were noted. Two patients reported short-lasting nausea, one vomiting, one constipation and in 2 patients, orthostatic dizziness occurred after the first injection. Subsequent injections, however, were well tolerated systematically and locally. Five patients had CT scan evidence of tumour shrinkage. A very large tumour virtually disappeared after the first injection of 50 mg depot-bromocriptine in one patient. The decrease of serum PRL secretion within the first 12 hours after injection did not predict normalization of serum PRL levels during long-term treatment, whereas the fall of serum PRL levels to below 5% of the basal values within the first months of treatment could be a good indicator for the final outcome.