Double immunodiffusion were used as screening test for the diagnosis of paracoccidioidomycosis. Five hundred hospitalized adults from general (150 patients -group I) and from a specialized chest disease hospital (350 patients -group II), were tested. All of them were without definitive etiological diagnosis and clinical specimens were obtained from the patients with positive serology. Testing sera obtained from 150 patients of the group I, fifty six cases of paracoccidioidomycosis were diagnosed. Specimens for mycological examination were subsequently obtained from 50 of these patients; P. brasiliensis could be recovered in 49 (98~ Fundamental importance was the finding of 17 (4.807o) cases of paracoccidioidomycosis among the 350 patients referred from a chest disease hospital (group II). Serological evidence of paracoccidioidomycosis found in 73 (14.6070) of the 500 screened patients, indicates a relatively high prevalence of this mycosis in adults patients admitted to several hospitals in RJ. These data probably do not reflect the real prevalence of paracoccidioidomycosis in RJ and should be considered as a gross underestimation. Thus, attention should also be paid to juvenile forms and DID could be of a great value in screening these cases too, * This work forms part of the thesis 'A import~ncia das t6cnicas de imunoprecipitagfio na triagem e diagn6stico da paracoccidioidomicose, histoplasmose e aspergilose. Estudo em populac~o hospitalar do RJ'. M. Phil. on Parasite Biology, Instituto Oswaldo Cruz, RJ -1984.