there has recently been evidence of a close association between the central nervous system and immune system but, not many drug-free studies exist. We have studied lymphocytes, immunglobulins and cortisol levels in 40 drug free patients with depression and mania, and in the control group consisting of 20 healthy volunteers,matching in sex and age to the study group. We found a significant decrease in T cell population (CD3) and CD4 proportion in both patient groups compared to the control group. Significant decrease in CD8 proportion of T lymphocytes was found only in depressed patients while there was not a statistically significant difference between B (CD19) cell percentages in both patient groups compared to the control group. IgG levels were significantly high in both patient groups, but there was no difference in IgA levels amongst all. IgM levels were significantly high in patients with mania and were significantly low in depressed group compared to the control group. There was not a statistically significant difference in cortisol levels and no relationship was found between the cortisol levels and immune parameters. These data provide evidence for a direct pathway through which mood disorders may cause alterations in immunity.