The imino-thiazolidine derivative EGYT-4201 exhibited marked activity in pharmacological tests characteristic for antidepressants. In the behavioral despair model and in antagonizing the effect of tetrabenazine its efficacy was considerably higher than that of several tricyclic and second generation antidepressant drugs. The compound also proved to be active in inhibiting the hypothermic effect of apomorphine. It potentiated the lethal effect of yohimbine, the hypermotility provoked by L-dopa, and the stereotypy induced by D-amphetamine. In contrast to amitriptyline and nomifensine, EGYT-4201 showed neither sedative nor stimulant actions on spontaneous and conditioned behavior. The compound, similar to amitriptyline and viloxazine, exerted a moderate anticonvulsive effect against pentylenetetrazole, bicuculline, and picrotoxin. EGYT-4201 did not exhibit significant anticholinergic activity on physostigmine induced lethality, oxotremorine evoked tremor, and isolated guinea pig ileum. In acute toxicity studies it proved to be more favourable than the reference compounds. EGYT-4201 did not inhibit the enzymatic activity of the monoamino-oxidase (MAO) enzyme, nor did it block the uptake of monoamines. The molecule was found to be inactive in binding studies of noradrenergic, dopaminergic, and serotonergic receptor types.