We performed the Irwin test on some different extracts of the aerial parts of Tridax procumbens L., of the leaves of Neurolaena lobata (L.) R. Br., of the bark and leaves of Byrsonima crassifolia (L.) Kunth. and Gliricidia sepium Jacq. Walp. and of the root and leaves of Petiveria alliacea L. At a dosage of 1.25 g extract/100 g dried plant, the aqueous extracts of bark and leaves of Byrsonima crassifolia (L.) Kunth. and G. sepium Jacq. Walp. showed higher activity: decrease in motor activity, back tonus, reversible parpebral ptosis. catalepsy and strong hypothermia.