Background. The aim of the study was to search for the existence of, and define, a possible relationship between performance in neuropsychological tests and baseline concentrations of plasma cortisol, vasopressin and oxytocin in medication-free patients with a major depressive episode.

Methods. Measures of depression and anxiety were obtained and a neuropsychological battery was presented. Blood for neuropeptide analysis was drawn by venepuncture at 8.00, 16.00 and 23.00 h.

Results. The melancholic patients performed less well on the neuropsychological battery than did the non-melancholic patients, but these differences could be accounted for by the severity of the illness. Global intellectual functioning was negatively correlated with mean baseline plasma concentrations of cortisol. Patients with high mean plasma vasopressin concentrations remembered more auditory presented words in the delayed recall test and produced more intrusions in the visual word learning list than did patients with low or normal mean plasma vasopressin concentrations. No association was found between neuropsychological performance and plasma concentrations of oxytocin.

Conclusions. Our findings support the hypothesis that elevated baseline plasma cortisol concentrations are related to cognitive impairment in depressed patients and the hypothesis that the neuropeptide vasopressin independently enhances memory, directly or indirectly through increasing arousal and attention.