PIP: For the last 5 centuries in Mexico the zoapatle aqueous crude extract (ZACE) has been used for the induction of labor, treatment of postpartum bleeding problems, and as a menses inducer. Despite widespread and continuous use of ZACE on the part of the Mexican population and the absence of documented side effects or toxicological phenomenon associated with its use, it was decided to undertake acute and subacute toxicological studies prior to clinical studies in volunteer subjects in Mexico and Sweden. Plant specimens for the studies were collected in different batches at several locations near the National University of Mexico. The material was properly identified at the university's botanical herbarium. ZACE was prepared by boiling 100 g of dry leaves in 400 ml of distilled water for 20-30 minutes, filtered through gauze, and the final volume obtained by using a rotor evaporator 50-60 degrees Centigrade with light negative pressure, to 100 ml. The ZACE concentration was 1 g dry leaves/ml. The extract was tested in an "in vitro" guinea pig uterine strip assay. For the 1st series of studies in Mexico, 60 female Sprague-Dawley rats, 8 weeks old, and 6 mongrel female dogs, were used. 25 rats were used as control and 35 tested. All animals were maintained in a controlled laboratory condition with 12/12 hour light/darkness cycle. 2 dogs served as control, and 4 were treated. All experimental animals received, through a rubber cannula, 5 ml/KG of ZACE daily. Control animals received distilled water. Each animal was carefully observed for 30 minutes after fluid intake. At the end of the study, the rats were sacrificed with ether, and the dogs with phenobarbital. Complete anatomapathological examinations were performed. 6 control and 8 treated rats died during the study, and all deaths were associated with accidental placement of the rubber cannula. Behavioral changes were observed in neither rats nor dogs throughout the study. No changes were recorded in body weights. No macro nor microscopic alteration was found in either group of rats. Results of hematological examinations did not differ between the 2 groups. It was concluded that ZACE is devoid of acute and subacute toxicity. In addition to the clinical observations reported by Gallegos in Mexico, where 10 normally menstruating volunteer women received 15 or 30 gm/day of zoapatle dry leaves extract orally for 3-9 consecutive days without clinical evidence of any side effects, clinical investigations were conducted by Landgren et al. in Sweden. 6 women in early pregnancy were given zoapatle; 6 women in early pregnancy served as a control group. A significant dilation of the cervix was found in each of the subjects treated with zoapatle decocts. A menstrual like cramp was reported by all and bleeding occurred in 4 of 6 subjects. No gastrointestinal symptoms were observed. No pain or bleeding nor significant dilatation of the cervix was evident prior to surgery. Immediately prior to vacuum extraction, cervical dilatation was less than 5 mm in all subjects. In sum, ZACE was devoid of toxic complication or side effects.