Fifteen patients with hyperprolactinaemia and pituitary macroadenomas (5 patients), microadenomas (6 patients), or acromegaly (4 patients) were given a single intramuscular injection of 50 mg bromocriptine bound to polylactic acid microspheres, depot-bromocriptine. None of the patients had any short-term or long-term discomfort from the injection. In the 11 patients with prolactinomas, serum prolactin fell to minimum levels 12-72 h post-injection; nine patients were highly responsive to depot-bromocriptine, with a mean serum prolactin of 12.9% of basal levels 24 h post-injection, rising to 19% at 28 days. Two patients with prolactinomas were resistant to both depot-bromocriptine, and large doses of oral dopamine agonists. Initiating side-effects (nausea, vomiting, symptomatic postural hypotension) were seen in five patients in the first 24 h post-injection, but were minimal or absent thereafter. Five of six patients previously intolerant of oral dopamine agonists were able to be transferred successfully to bromocriptine 5 mg daily at 4 weeks. Of the four patients with acromegaly, raised prolactin levels were successfully lowered to normal for 4 weeks after injection; serum GH was also partially lowered, but returned to baseline levels at 2-4 weeks. In one patient serum GH was resistant to suppression by both depot bromocriptine and high doses of oral bromocriptine. One patient with a large tumour and visual field defects showed a rapid and maintained improvement in visual fields and acuity after depot-bromocriptine, and was successfully transferred to high-dose oral bromocriptine at 4 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)