Evaluation of mutagenicity and antimutagenicity of different fractions of Pterogyne nitens (Leguminosae), using Tradescantia pallida micronuclei assay. Pterogyne nitens (Fabaceae-Caesalpinioideae) is a tree native to South American, where it is used in folk treatment of ascaridiasis. Recently, we have been describing the mutagenic. effect of the ethanol extract of leaves of P. nitens. Thus, the present study aimed at evaluating the mutagenic potential of the ethyl acetate (EtOAc), n-butanol (BuOH) and hydroalcoholic (HA) fractions., When the mutagenic effect was observed only, in the highest tested concentrations, the antimutagenic activity was also evaluated. Both mutagenic and antimutagenic assays were performed using T. pallida micronuclei assay. Mutagenicity was observed between different concentrations of the P. nitens fractions, EtOAc (0.460 mg/mL), BuOH (0.142, 0.285, 0.570 and, 1.14 mg/mL) and HA (0.050, 0.100, 0.200 and 0.400 mg/mL). Whereas the mutagenic effect of the EtOAc was observed in the highest concentration (0.460 mg/mL), its antimutagenic potential fraction was evaluated. The 0.115 and 0.230 mg/mL concentrations of the EtOAc fraction demonstrated antimutagenic activity. Based on the results of the present study We can conclude that some P. nitens fractions (BuOH and HA) demonstrated, mutagen id effects whereas the - EtOAc fraction shown low mutagenicity and antimutagenicity in the two higher concentrations. Those results stimulate the studies with P. nitens, which possess spread geographic distribution and it is still low studied.