In order to correlate the findings of two serological tests, double immunodiffusion (IDD) and immunoblotting (IB), with the clinical diagnosis and follow-up of paracoccidioidomycosis (PCM), 325 serum samples from PCM patients were tested at the beginning of specific therapy and after its completion. Group I included 245 PCM patients at the onset of symptoms without treatment. In 221 cases (90.2%) the IDD showed positive reactions and in 24 (9.8%) the results were negative. Of the 24 IDD negative samples, 23 were investigated by IB and were positive. Group II included 80 PCM patients under follow-up after treatment. There were four cases of relapse in which the IDD and IB tests were positive (100%). Among the 76 cases with inactive mycotic infection, the IDD was negative in 71.2% and positive in 28.8%; the IB was positive in all cases (100%). The control group (Group III) included 27 samples from patients with other mycoses, tuberculosis and from healthy individuals. All showed negative IDD tests but positive reactions with IB, which could be abolished by serum dilutions without altering the PCM reactivity. Therefore, the utilization of the IB, an immunoenzymatic method for the diagnosis of PCM, raised the sensitivity to 100%.