An atypical strain of Paracoccidioides brasiliensis was obtained from a patient with disseminated paracoccidioidomycosis. This isolate, which has been maintained in the laboratory for 4 years by successive subcultures (30-40 days) in Fava Netto medium, produces cerebriform colonies characteristic of the yeast phase of the fungus when left at room temperature. Microscopy shows a predominance of yeasts with multiple buds, side by side with some branching filamentous structures presenting intercalary chlamydospores. The strain does not develop well at 37 degrees C, suggesting heat sensitivity. Storage at 4 degrees C does not change its macro- or microscopic characteristics. These findings support the hypothesis raised by others that the dimorphism of P. brasiliensis may not be exclusively heat dependent. Studies are currently being developed in our laboratory to better characterize this isolate in terms of biochemical peculiarities, degree of virulence and susceptibility/resistance to antifungal drugs.