Abortive effects on cattle have been attributed to Piper sp, popularly called Pariparoba. In the present study we tested the possible toxicity of this plant by analyzing gestational outcome parameters in female rats given 300 mg/kg of an aqueous extract of Piper sp leaves and stalks per os, daily, between the 9th and the 21st day of pregnancy. The animals were killed just before delivery and the following features were observed: numbers of corpora albicantia, fetuses and reabsorptions; weights of fetuses, placentae and fetal membranes; fetal sex and the presence of overt malformations in fetuses; and implantation and reabsorption indices. No significant differences were detected between control and treated groups. The results suggest that Piper sp does not modify gestational outcome in rats.