The pathology of neurotransmitters is of the key importance in the pathogenesis of multiple sclerosis. The developed method makes it possible to determine, with a high accuracy degree, the level of gamma-aminobutyric acid (GABA) and the activity of glutamate decarboxylase (GAD) in the blood serum of patients with multiple sclerosis. The study showed that the level of neurotransmitters and the GAD activity in the blood serum of patients was reduced as compared to the controls. The neuronal transmission pathology can have the key importance in the development, progressing and clinical course of the demyelization process.