Lobomycosis and paracoccidioidomycosis are two different mycoses caused by Loboa loboi and Paracoccidioides brasiliensis, respectively. To verify cross-antigenicity between them, lobomycosis sera were tested by immunoblotting, ELISA and capture-EIA against crude exo-antigen, 'cell-free antigen' and gp43 from P. brasiliensis. The majority of lobomycosis serum samples recognized crude exo-antigens and gp43 from P. brasiliensis. Gp43 was eluted from an affinity column prepared with IgG from a patient with active lobomycosis. In lower frequencies and intensities, lobomycosis sera also recognized proteins of 29 kDa, 36 kDa, 39 kDa, 52 kDa, 63 kDa, 70 kDa, 83 kDa, and 108 kDa from P. brasiliensis.