Two derivatives of wax D, one possessing immunogenicity and the other adjuvant activity, were tested for the possible role in the induction of adjuvant arthritis (AA) in rats. The former, a water-soluble arthritogenic and immunogenic component (WAC), in incomplete Freund's adjuvant, was able to induce delayed hypersensitivity (DH) and mild AA, but failed to function as an adjuvant in rats. The latter, an acetylated wax D (AD) and its subfraction, AD6, did exert adjuvant activity, but were free from immunogenicity and arthritogenicity. The addition of AD or AD6 to the WAC in incomplete Freund's adjuvant, when injected into inguinal lymph nodes, resulted in the production of severe AA with high incidence. Other adjuvants such as pertussis vaccine and lipopolysaccharide could not replace AD6; they failed to enhance AA when combined with the WAC. Also, other mycobacterial antigen, PPD, could not replace wax D-derived WAC; it did not induce AA when coupled with AD6, although it did induce DH to PPD.