Following the success of ergot alkaloids and their synthetic derivatives in treating a variety of pathophysiological disturbances, efforts have been concentrated on the synthesis of new derivatives and partial structures with the aim of dissecting out a specifically dopaminomimetic pharmacophore. Accordingly CV 205-502, a structure which superposes the linear benzo [g] quinoline segment of apomorphine on the substituted pyrrolo [3,4- g] quinoline moiety of the ergolines was designed. This study was performed in normal young volunteers to investigate the effect of single oral doses of CV 205-502 on plasma prolactin levels and on other endocrine parameters (GH, LH, FSH, TSH and cortisol) as well as on tolerability. 10 volunteers participated in a dose-ranging study. They received single oral doses of 0.01 to 0.09 mg CV 205-502, in order to assess the prolactin suppressant action. 6 volunteers were given a dose of 0.06 mg CV 205-502 in order to determine the endocrine profile of the compound. The duration of action of 0.06 mg CV 205-502 was investigated in 6 subjects by measuring plasma PRL and GH levels for 48 h. The results show strong dose-dependent suppression of PRL appearing following doses between 0.04 and 0.09 mg of CV 205-502. PRL was markedly suppressed for more than 24h. and the peaks of the normal sleep profile were abolished. Intermittent transient GH increases occurred during the first 6 hours; sleep profiles were normal. Compared with placebo values, no changes were seen in the levels of any other hormone except TSH, which decreased. Tolerability was good and no drug attributable changes in safety measures occurred. This study demonstrates that CV 205-502 is a potent and long acting PRL suppressant compound and suggest that this novel octahydrobenzo [g] quinoline will prove to be a therapeutically useful dopaminomimetic compound.