A human isolate (IVIC Pb73) of paracoccidioides brasiliensis and a mutant strain (IVIC Pb219) derived from Pb73 were studied with regard to their cell wall composition. Differences were found between these strains and the only other strain (IVIC Pb9) previously studied from this point of view. Besides the expected beta-1,3-linkages, beta-1,2-bonds were also found in the alkali-insoluble glucan of both the parental and the mutant strains in the yeast forms, a rather uncommon linkage in fungal glucans. Also, the alkali-insoluble fraction from the mycelial form was composed of glucose (of which a very small proportion occurred as beta-1,3-glucan) plus a high proportion of galactose (about 50%), and some mannose. The alkali-soluble fraction, usually associated with the immunogenic galactomannan in the mycelial form, also had glucose besides galactose and mannose, but was exclusively composed of mannose in the yeastlike form. These results suggest that, as in other fungi, variations in cell wall composition could be expected between strains of P. brasiliensis.