The experiments presented in this paper aimed to investigate whether estrogen level changes in oviariectomized rats (OVX) may lead to depression and memory disorders, and whether the effects of such changes may be reversible following administration of a new antidepressant, venlafaxine (CAS 9930-78-4, VEN, Efectin). The Porsolt forced swimming test and Morris water maze test were carried out on female Wistar rats after ovariectomy and in sham-ovariectomized rats. VEN 20 mg/kg was administered orally 30 min before the tests for the period of 14 days. Estradiol (17beta-estradiol benzoate, CAS 50-28-2, E2) administration (5 microg E2/0.2 ml sesame oil s.c.) was started 24 h after ovariectomy and was continued for 14 days--each dose was administered 180 min before the test. In the immobility test, which reflects antidepressant drug activity, it was found that VEN shortened immobility time (IT) after the 1st, 7th and 14th administration (days 1, 7, 14, respectively) in ovariectomized rats, whereas in the control group (sham-ovariectomized rats) VEN exerted antidepressant action only after single administration (day 1) and after 7 days of administration. E2 significantly reduced immobility behaviour both after single and chronic treatment in ovariectomized rats. After joint administration of VEN and E2 potentiation of the antidepressant activity of VEN could be observed in both groups except for concurrent administration of VEN and E2 after 14 days in sham-ovariectomized rats. VEN improved the spatial memory in the Morris water maze test, whereas E2 did not affect the memory of the tested animals. Joint administration of VEN and E2 maintained the memory improving effect induced by VEN. The regulatory role of the steroid hormone and the new antidepressant drug (VEN) in antidepressant activity and memory function could be related to the interactions between noradrenergic and serotoninergic systems.