Fonsecaea pedrosoi, a dematiaceous fungus and the main causative agent of chromoblastomycosis, has been isolated in worldwide from different natural sources in regions where the disease is endemic. In the Amazon region of Maranhão, Brazil, where the disease is prevalent, the breaking of the babassu coconut (Orbignya phalerata Martius) represents an important agricultural activity. In order to determine the presence of this fungus on this plant and on other natural substrates, material was collected in the Fortaleza Village Municipality of Pinheiro, Maranhão, in April and September 2002. A total of 68 samples, including 18 (26.5%) obtained from the shell of the babassu coconut, were analyzed. Samples were cultured using a standard method. Isolates were identified based on macromorphological aspects of the colonies on Sabouraud dextrose agar and based on the micromorphology of the conidia after growth on potato dextrose agar. Exophiala sp. was the most prevalent fungus isolated from the different natural substrates analyzed, while Cladophialophora sp. was only isolated from decomposing wood. Fonsecaea pedrosoi was isolated from one sample of babassu coconut shell suggesting that this coconut represents an important source of infection of chromoblastomycosis during extraction of the plant product in this region.