Exoantigens from cultures of Paracoccidioides brasiliensis were separated by SDS-PAGE and subsequently blotted onto nitrocellulose paper. Immunologically reactive components were detected by reaction with sera from patients with paracoccidioidomycosis (PCM). Peroxidase-conjugated anti-human IgG was used as a detector antibody to reveal immunocomplexes. Anti-P. brasiliensis IgG reacted with four major components of 70, 52, 43 and 20-21 kDa and with eight minor components. The 43 kDa glycoprotein (gp) was the predominant IgG reactive antigen, recognized by 100% of the patient's sera. The antibody titre to the 70 kDa glycoprotein, recognized by 96% of the sera tested, decreased significantly in patients undergoing antimycotic therapy. Cross-reactions with the immunoblotting technique could be minimized by serum dilution. Both gp 43 and gp 70 can be considered to be markers for human PCM under the test conditions used in our immunological assay.