Pergolide is a synthetic ergoline derivative with highly potent long-acting PRL-lowering activity, allowing therapy of hyperprolactinemia with a once daily administration of the drug. The results of two open-label, randomized controlled multicenter clinical trials are reported. Pergolide (taken once a day), was compared with bromocriptine (taken two to four times daily) regarding efficacy and safety in the reduction of PRL levels, the cessation of galactorrhea and amenorrhea, the improvement in sexual function, and tumor shrinkage in hyperprolactinemia without (trial I; 61 patients) and with radiologically evident pituitary tumors (trial II; 96 patients). Both drugs were equally effective in lowering PRL levels in both trials. A median optimal dose of 50 micrograms pergolide and 5 mg bromocriptine/day suppressed PRL levels in the 61 patients of trial I by more than 80%. During the 24-week investigational period galactorrhea disappeared in 96% and 87% of patients, whereas menstruation returned in 90% and 96% of patients, respectively. An equally high efficacy (optimal median dose: 75-100 micrograms pergolide, 7.5-10 mg bromocriptine daily) was observed in trial II, although the resumption of menses was less frequent than in the patients of trial I (50% and 58% of patients, respectively). Sexual dysfunction improved similarly on both drugs in about half the patients. In addition, tumor shrinkage occurred to a similar extent with both drugs. A high incidence of adverse events was noted especially at the initiation of therapy with both compounds: nausea, dizziness, vomiting, asthenia, headache, and decrease in blood pressure occurred at a similar incidence and extent during the use of pergolide and bromocriptine. Patients in trial I treated with pergolide reported a slightly higher incidence of fever, vasodilatation, and flu syndrome. CONCLUSIONS in these 24-week studies comprising a total of 157 hyperprolactinemic patients, a once daily administration of pergolide was shown to be as safe and effective as the two to four times daily ingestion of bromocriptine. Longer-acting dopamine agonists like pergolide that can be taken once daily, are likely to increase the ease to adherence to the therapeutic regimen. This might result in a higher compliance to medical treatment of hyperprolactinemia.