Fumonisins are mycotoxins produced mainly by Fusarium verticillioides, which can modulate the immune response. Paracoccidioidomycosis (PCM), caused by the fungus Paracoccodioides brasiliensis (Pb), is one of the most important systemic mycoses in Latin America. The aim of this study was to evaluate the effect of the partially purified fumonisins on cellular immune response in mice infected with Pb. Four groups of male BALB/c mice were used. Groups PB and PB/FB were inoculated i.v. with 1 × 105 Pb yeast cells and, after 28 days, groups FB and PB/FB were inoculated (s.c.) with partially purified fumonisin B1 from F. verticillioides (5 × 2.25 mg FB1/kg body weight). After 7 days, cellular immune response was evaluated by delayed-type hypersensitivity (DTH) and lymphoproliferative assays (LA) using spleen cells. Nitric oxide (NO) production by spleen cells was also evaluated. The specific LA response to Pb antigen was higher in group PB than in FB and CTR groups (p< 0.05) but not significant with PB/FB. The DTH response was higher in infected than non infected groups (p<0.05) but also no significantly with PB and PB/FB groups. The lyphoproliferative response to ConA was decreased in FB or PB/FB in relation to CTR (p<0.05) but not with PB/FB and also a reduction of NO levels was observed in fumonisin treated in relation to control group FB1/kg (p<0.05). In conclusion, fumonisin B1 or other components of F. verticillioides extracts significantly suppress the unspecific cellular immune response and the NO production by splenocytes from P. brasiliensis infected or not infected BALB/c mice.