This presentation discusses links between mood disorders and temperament traits. The assessment of temperament utilized the Compact version of STQ (STQ-77) based on Trofimova's Functional Ensemble of Temperament model. The 12 temperament scales of the STQ-77 include 3 emotionality scales (Neuroticism, Impulsivity, Self-Confidence) and 9 scales measuring dynamic aspects of activity (endurance, programming-integration and orientation) analysed separately for physical, social and intellectual activities. Emotionality is presented in this model as an amplifier of the arousal, lability and orientation aspects of activity. The point of discussion will focus on the contribution of biological and temperament factors to mood disorders. The study is based on the administration of the Compact STQ-77 to156 healthy Canadian subjects and to clinical samples of 307 patients diagnosed with anxiety and depressive disorders. Significant correlations were found between 9 temperament traits and the presence of depression and between 3 temperament traits and the presence of anxiety. Putative links between the presence of anxiety and depression and dysfunction in mu and kappa opiod receptor protein systems will be discussed.