SumaryThe medicinal plant Jacaranda decurrens Cham., known as "carobinha-do-campo", is native to "Cerrado" (open pasture land with patches of stunted vegetation, woody pasture) and it belongs to the family Bignoniaceae. It is used in the popular medicine for the syphilis treatment, diaphoresis, inflammations etc., being prepared in the form of infusions (leaves and bark). We evaluated the mutagenic and antimutagenic activity of J. decurrens in somatic cells of Drosophila melanogaster using the SMART/eye test (somatic mutation and recombination test), which is based on the pigmentation of Drosophila ommatidia. Deletions, point mutations, non-disjunction and somatic recombinations were detected. Larvae in the third instar, resulting in crossing between virgin females from the Yellow lineage and males from the White one were treated with three different concentrations of J. decurrens ethanolic gross extract (EGE): 10 mg/ml (dosage-1); 6.25 mg/ml (dosage-2) and 4.16 mg/ml (dosage-3). They were isolated for mutagenic activity evaluation and associated to urethane (URE) for the antimutagenic analysis. URE was used (4 mg/ml) for the positive control and distilled water for the negative one. Three experiments were carried out for both mutagenesis and antimutagenesis. In the evaluation of the mutagenesis, the amount of clones/cells found in the dosage-3 (10.14) was statistically significant when compared to the negative dosage control (2.31), leading to the conclusion that J. decurrens EGE has a mutagenic effect depending on the concentration. On the other hand, in the antimutagenetic analysis, the EGE showed an antimutagenic effect in the three concentrations (dosage-1ϭ4.18; dosage-2ϭ4.58; and dosage-3ϭ3.24 clones/cells) when compared to the positive control (urethaneϭ6.29 clones/cells). Compared to dosage-3 (more diluted), the EGE presented a larger modulator effect of the genetic damages caused by URE. Thus, considering the established experimental conditions, we concluded that J. decurrens EGE has, depending on the concentration, either a mutagenic effect or a protecting effect of DNA against URE damage.Key words Mutagenis, Antimutagenesis, Drosophila melanogaster, Jacaranda decurrens, SMART/eye.The use of medicinal plants (phytotherapy) is the result of the amount of secular empirical knowledge about the plant actions in several ethnic groups. Therefore, there are many questions