Major depression is a serious disease with various systemic effects, including 
dysfunction of the immune response. Taurine has been known to be related to 
certain modifications of the immune system. The aim of this study was to 
determine the taurine concentration in lymphocytes of patients with major 
depression and to evaluate the influence of the antidepressant treatment with 
mirtazapine for six weeks on the levels of taurine. Gamma-aminobutyric acid, 
aspartate, glutamate and glutamine were also determined. Taurine, aspartate and 
glutamine levels were increased in the lymphocytes of depressed patients before 
mirtazapine treatment compared to the control group, and were normalized after 
treatment. Gamma-aminobutyric acid and glutamate did not differ between patients 
and controls. There was a significant and positive correlation between the 
severity of the disorder, measured by the Hamilton Rating Scale, and the 
concentration of taurine in the lymphocytes of depressed patients before 
treatment. This correlation was not observed after treatment and neither was 
there a correlation observed for the other amino acids. The present observations 
could be an indication of the relevance of taurine as a protective agent in the 
lymphocytes of patients with severe depression, and could be the result of 
modifications of taurine transport or efflux processes.