The method of enzyme immunoassay (ELISA) was used for detection of antibodies against the basic protein myelin (antimyelin antibodies) for a group of serum samples (n 36) with positive anti-borrelia immunoglobulins IgG and IgM (ELISA-Borrelia afzelii) and their immune complexes (ELISA-PEG). Antimyelin antibodies (ELISA-Doxa Kit-Myelin Basic Protein Antibodies) were assessed in 31% (n 11) of examined serum samples of patients with the working diagnosis of Lyme borreliosis. Statistical analysis (p 0.07) confirmed a more frequent incidence of antimyelin antibodies in younger female subjects (age 31 years) as compared with a group of sera (n 25) where the authors did not record the formation of immunoglobulins against the basic myelin protein (age 51 years). Neither the value of titres nor the frequency of detected anti-borrelia IgG and IgM and immune complexes did not differ significantly in the two groups. From the assembled results ensues that in the course of Lyme borreliosis, in chronic affection of organs an autoimmune reaction may develop where the basic myelin protein is damaged (demyelinizatio) and subsequently antimyelin antibodies are formed.