A complex neurological and neuropsychological examination, including the detection of depression, was conducted in 71 patients with multiple sclerosis aged from 23 to 62 years (mean age 43 ± 9 years). An immunobiochemical study included the analysis of expression of CD80 and CD86 on monocytes and B-cells, expression of TLR2 and TLR4 on monocytes, expression of D3 and D5 dopamine receptors on monocytes and B-cells, using flow cytometry, and the determination of Il-6, Il-10, IL-12p40 and dopamine plasma levels as well as vanillylmandelic acid (VMA, dopamine metabolite) urine levels measured with immunoenzyme assay. The results suggest the involvement of dopamine in the pathogenesis of depression in MS as assessed by dopamine and its metabolites levels. The role of dopamine and monocyte activation (by TLR2) in the pathogenesis of cognitive disturbances was specified as well.