Brain proteome analysis of mice selectively bred for either high or low anxiety-related behavior revealed quantitative and qualitative protein expression differences. The enzyme glyoxalase-I is consistently expressed to a higher extent in low anxiety as compared to high anxiety mice in several brain areas. The same phenotype-dependent difference was also found in red blood cells with normal and cross-mated animals showing intermediate expression profiles of glyoxalase-I. Another protein that shows a different mobility during twodimensional gel electrophoresis was identified as enolase phosphatase. The presence of both protein markers in red or white blood cells, respectively, creates the opportunity to screen for their expression in clinical blood specimens from patients suffering from anxiety.