Depression and anxiety were examined by Hospital Anxiety and Depression Scale and Spilberger Scale in 217 multiple sclerosis patients treated by Betaferon. The concentration of blood serotonin was determined by immunoenzyme analysis in 71 of them. The multiple sclerosis patients had progressive high levels of depression ((7,55 ± 3,61) points; р = 0,000) and anxiety ((7,55 ± 3,61) points; р = 0,000), and the decreased blood serotonin concentration ((210 ± 134,2) versus (269 ± 98,8) ng/ml; р = 0,036 in healthy people). The level of anxiety was related to the level of serotonin depression. Betaferon did not correct the affective disorders in multiple sclerosis patients, except the decreasing the degree of anxiety, and did not normalize the level of blood serotonin, that suggest the use of selective serotonin reuptake inhibitors during immunomodulating therapy.