Plasma levels of the partial dopamine agonist, terguride, were measured by RIA in healthy volunteers after a single i.v. dose of 50 micrograms and on the first and seventh day of an oral treatment with 250 micrograms, 500 micrograms and 750 micrograms b.d. Basal and releasing hormone (TRH, GHRH, CRF, LHRH)-stimulated pituitary hormone secretion (PRL, TSH, GH, FSH, LH) and cortisol were also determined by RIA. Following the i.v. injection, plasma terguride levels declined biphasically, with half-lives of 0.2 and 1.5 h; total clearance was 17 ml.min-1.kg-1. The oral bioavailability of terguride over all doses was about 20%. Basal and TRH-stimulated prolactin levels were dose-dependently depressed, but the secretion of other hormones remained unaffected. Tolerance of terguride was excellent and there was no negative effect on performance or mood, nor on mixed-function oxygenase activity, assessed as urinary 6 beta-OH cortisol.