Trazium is a putative antidepressant compound with special pharmacological effects on the catecholaminergic systems. Trazium esilate (EGYT-3615) is structurally an as-triazino isoquinolinium salt which showed considerable activity in pharmacological tests characteristic for antidepressants (antagonism of tetrabenazine, potentiation of yohimbine, behavioral despair). The compound exhibited the minimal sedative effect. The drug potentiated actions of amphetamine such as stereotypy and hypermotility. It differentially blocked the hypothermic and the stereotypy inducing action of apomorphine. Trazium esilate also inhibited the cataleptic state provoked by bulbocapnine in mice. In higher dose it decreased the plasma prolactin level in rats. Trazium esilate is a weak displacer on a1-, a2- and D2-receptors, however, it induced a2-receptor desenzitization after repeated treatment. Trazium bounds to the serum proteins and the binding was sensitive to pH and salt concentration. The binding of trazium was not saturable at a wide range of drug concentration. Trazium has both specific and non-specific binding sites on serum proteins.