The discovery of reliable biomarkers for psychiatric disorders such as major depressive disorder (MDD) could help to improve diagnosis and treatment. The authors used two animal models of depression to identify 26 candidate biomarker transcripts and compared their expression in human subjects with and without early-onset MDD. The expression of 11 of these transcripts differentiated patients with MDD from controls, suggesting that this approach might yield a reliable panel of biomarkers for the disease.