Paracoccidioides brasiliensis (Pb) is the dimorphic fungus responsible for paracoccidioidomycosis (PCM), one of the most important systemic mycosis in Latin America where the disease is geographically restricted. The natural habitat of the causative agent remains undetermined. We are planning to use PCR-based technology in order to amplify specific DNA fragments. The high sensitivity of this technique may allow us to detect the natural habitat of Pb. In this study, we prepared a cDNA library from which we cloned a protein of approximately 27 kDa MW. When this recombinant antigenic protein was tested by the immunoblot technique, it was able to recognize antibodies in the sera of 91% of the PCM patients studied. No cross reactions were observed with sera from patients with other systemic mycoses. Presently we are sequencing and characterizing this clone, in order to design specific primers for amplification of Pb DNA.