Dark August rats exhibit clinically and histologically verified experimental allergic encephalomyelitis (EAE) when immunized with appropriate antigen (nervous tissue, myelin basic protein) emulsified in complete Freund's adjuvant (CFA). We provide evidence that 6,6'-trechalose dymicolate (TDM) incorporated in incomplete Freund's adjuvant replaces CFA in EAE induction. The animals that recovered from EAE were resistant to the reinduction of the disease irrespectively whether Mycobacterium tuberculosis or TDM was used as an adjuvant. Finally, pretreatment with CFA alone was sufficient for prevention of disease elicited by challenge with encephalitogen + CFA. However, TDM, despite its adjuvant capacity when applied prior to the induction of the disease with encephalitogen + CFA, did not exhibit any protective effect. Thus, our study implicates that adjuvant and suppressive capacities of M. tuberculosis may be related to the different determinants of the microorganisms, TDM possessing the adjuvanticity only.