This is the first report on proteomic analysis of the cerebrospinal fluid (CSF) in unmedicated suicide attempters and non-attempters with major depressive disorder. Two-dimensional (2D) gel electrophoresis revealed that suicide attempters differed from non-attempters in one protein with an approximate molecular weight of 33 kD and an isoelectric point of 5.2. Proteomic analysis of the CSF is a promising non hypothesis-driven screening method for the detection of new candidate genes in neurobiological suicide research.