Vascular endothelial growth factor (VEGF) has been implicated in neuronal survival, neuroprotection, regeneration, growth, differentiation, and axonal outgrowth, which are known to be involved in the pathophysiology of major depressive disorder (MDD). Recently, the VEGF mRNA expression in the peripheral leukocytes from Alzheimer's disease or cardiovascular disease was reported to be changed. We hypothesized that the expression of the VEGF mRNA in the peripheral leukocytes may be a good candidate for the biological marker for MDD. Thirty two patients with MDD and age- and sex-matched control subjects were included in this expression study. The VEGF mRNA levels in the peripheral leukocytes from drug-naive MDD patients were significantly higher than those from the control subjects and the magnitude of the decrease of VEGF mRNA after 8-week treatment significantly correlated with clinical improvement. Then, we genotyped two single nucleotide polymorphic markers of VEGF gene, which were reported to be associated with amyotrophic lateral sclerosis and Alzheimer's disease, in patients with MDD and control subjects (n=154, each). We did not find any significant association between these markers and MDD or its clinical subtypes. Our investigation indicates that the higher expression levels of VEGF mRNA in the peripheral leukocytes are associated with the depressive state and their recovery after treatment may be associated with the clinical improvement.