Evidence suggests that the neuropeptide oxytocin plays a role in social affiliation. This behaviour may be related more to personality dimensions than specific psychiatric diagnoses. This study investigated the relationship between plasma oxytocin levels and personality dimensions using the Temperament and Character Inventory (TCI) in 60 outpatients with major depression. The strongest correlation was between plasma oxytocin levels and the temperament dimension of Reward Dependence (0.425 Pearson correlation). This suggested that 17% of the variance in plasma oxytocin levels was explained by the Reward Dependence scores. There was a significant positive correlation between plasma oxytocin levels and the Reward Dependence personality dimension.