1. The effects of canatoxin, the toxic principle from Canavalia ensiformis seeds which has lipoxygenase-activating properties, were evaluated in rats using radioimmunoassay techniques to measure plasma levels of prolactin (PRL), progesterone, follicle stimulating (FSH) and luteinizing (LH) hormones. 2. The chronic administration of canatoxin (50, 100 or 200 micrograms/kg daily for 12 days, ip) to female rats induced a sharp rise in plasma LH and FSH concentrations with no changes in progesterone level. A fall in circulating PRL was also observed. The frequency of proestrus and weight gain increased in rats treated with the highest dose of toxin used, but there was no alteration in weight of uterus or ovaries. 3. The increases in gonadotropin levels with canatoxin are consistent with the lipoxygenase-activating properties of the toxin, but do not explain why plasma PRL concentrations decreased in canatoxin-treated rats. 4. Since the animals in the control group had high PRL and low LH levels and since canatoxin increased LH and decreased PRL in the circulation, a possible stress-prevention effect is discussed for the toxin. 5. This study supports previous suggestions of central actions for canatoxin, and indicates the hypophysis and/or hypothalamus as one of the target sites for the toxin in the central nervous system.