['We examined whether the aqueous extract of Erythrina falcata, reputed to be a contraceptive in Peruvian folklore, could prevent pregnancy in the mouse.', 'Female mice on Day 1 of pregnancy were given aqueous extract of E. falcata or tap water (control) orally for 4 days. On Day 4 of pregnancy, animals were killed and the embryos were flushed from oviducts and uterus to examine their developmental stage, cell number, mitotic index and micronuclei frequency. Other mice were killed on Day 12 of pregnancy to determine the number of implantation sites.', 'Ingestion of E. falcata diminished the percentage of embryos that progressed to blastocyst stage, reduced the cell number and mitotic index, and increased the micronuclei frequency of early embryos. The number of implantation sites was also reduced in females treated with E. falcata.'] Does postcoital ingestion of the aqueous extract of Erythrina falcata Benth prevent pregnancy in the mouse?