The involvement of central catecholaminergic neurons in tonic gonadotrophin release was investigated. Male rats were given a single cerebral intraventricular injection of 6-hydroxydopamine hydrochloride (6-OHDA; 170 μg free base) dissolved in 0·001 n-HCL. Plasma LH and FSH were measured by double antibody radioimmunoassay. In the 6-OHDA-treated animals, LH was significantly reduced (P<0·001 after 1 hr and remained consistently lower for 8 hr. After a transient elevation, the controls showed no significant change (P>0·01). No difference in LH concentrations was found between experimental groups sampled at 2 days or later (P>0·01). Levels of FSH were less consistently different. Administration of 6-OHDA dissolved in different vehicles, with varied pH and osmolarity, gave similar results which suggests that the quinone derivative of 6-OHDA is effective in producing the catecholaminergic impairment. These findings indicate that LH release in the male rat may be controlled (or at least modulated) by a central adrenergic mechanism.