The potential antidepressant properties of indeloxazine hydrochloride were examined in vitro and in vivo. Indeloxazine showed preferential affinity for both [3H] citalopram (Ki: 22.1 nM) and [3H]nisoxetine binding sites (Ki: 18.9 nM) in membranes of the rat cerebral cortex. In microdialysis studies, intraperitoneal injection of indeloxazine (3 and 10 mg/kg) dose-dependently increased the extracellular level of both serotonin and norepinephrine in rat frontal cortex of freely moving rats. Amitriptyline was almost equivalent to indeloxazine in these two assays with the exception of a much weaker effect on extracellular serotonin levels. Spontaneous [3H]serotonin release from rat cortical synaptosomes was significantly enhanced by indeloxazine (10-1000 nM). In behavioral studies, indeloxazine increased the number of wheel rotations in forced swimming tests in both ICR mice (50 mg/kg, p.o.) and SAMP8//YAN, a substrain of senescence-accelerated mouse (20 and 30 mg/kg, p.o.). Indeloxazine (3-10 mg/kg p.o.) also inhibited the incidence of muricide in raphe-lesioned rats. These results suggest that indeloxazine is an inhibitor of serotonin and norepinephrine uptake and has potential antidepressant properties. In addition, the drug-induced enhancement of serotonin release may contribute to its potent effects on the serotonergic system in vivo.