Nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) are proteins involved in neuronal survival and plasticity of dopaminergic, cholinergic and serotonergic neurons in the central nervous system. Since decreased size and impaired function of some neuronal populations may be relevant in depression it has been hypothesized that these molecules may have a functional role in the pathophysiology as well as treatment of depression. Using an animal model of depression, the Flinders Sensitive Line (FSL) rats and their controls, the Flinders Resistant Line (FRL), we investigated the effects of chronic lithium treatment on brain NGF, BDNF and GDNF. Lithium was administered as food supplementation during 6 wk. NGF, BDNF and GDNF measurements were performed by enzyme-linked immunosorbent assay (ELISA). Lithium altered the brain concentrations of neurotrophic factors in the hippocampus, frontal cortex, occipital cortex and striatum. Moreover, the changes were different in the two rat strains. Our data support the notion that neurotrophic factors play a role in depression and in the mechanism of the action of lithium.