The role of serotonergic systems in learning processes is even more controversial: For example serotonergic lesion have been reported to facilitate, impair, or have no effect on performance in various learning tasks. There are several possible explanations for these discrepancies; different importance of  confounding activation of different learning processes, different importance of confounding factors, such as anxiety on these tasks, lack of direct effects of serotonergic systems on learning processes and modulatory effects of other neurotransmitter on this system. Therefore we decided to test the effects of citalopram on passive avoidance learning (PAL) task. The experiments were performed on male albino rats (180-220gr). Citalopram was injected interaperitoneally at doses of 0.25, 0.5, 1,2, and 4 mg/kg. Citalopram was injected 30 minutes before training, or immediately after training, or 30 minutes before retrieval test. Control groups received saline. Our results indicate that citalopram has no effect on PAL acquisition but facilitates memory consolidation and retrieval. The maximal facilitatory effect was seen at  doses of 2 mg/kg. Citalopram has no effect on motor activity. Our results suggest that 5-HT has different effects on different steps of learning memory.