The present study aimed to assess the preclinical toxicity of two plants commonly used to treat “stomach ailments” in Brazil: Schinus terebinthifolius Raddi (S) and Myracrodruon urundeuva Allemão (M). In male rats, chronic treatment (83 days) with both pepper trees (17.6 and 13.8 mg/kg, S and M, respectively) has been shown to decrease hematocrit. However, a reduction in the number of red blood cells and hemoglobin was only seen following administration of S. terebinthifolius. None of the plants caused anatomopathological alterations following chronic treatment, and mating ability and fertility were not affected. Both pepper trees showed moderate toxicity following acute and chronic treatment by gavage, particularly S. terebinthifolius. Moreover, bone malformations were induced in fetuses, and a slight delay in recovery time of the postural reflex was observed in pups from female animals treated (18 days) with S. terebinthifolius. Given these results, a better assessment of the risks and benefits of the internal use of these plants is necessary, especially when used by women of childbearing age. Copyright © 2012 John Wiley & Sons, Ltd.