The aim of this study was to evaluate the efficacy of treatment of Lewis rats with calf thymus extract (TFX®) and its six-peptide fraction on the course of experimental allergic encephalomyelitis (EAE). Interferon- ß served as a reference drug. We found that intramuscular administration of the thymus extract fraction significantly reduced clinical, immunological, histological, and ultrastructural alterations inherent in the disease. We suggest that TFX® or TFX®-derived fractions have potential as therapeutics in treatment of neurodegenerative diseases such as multiple sclerosis.