Cerasee, a wild variety of Momordica charantia is traditionally prepared as a tea for the treatment of diabetes mellitus in the West Indies and Central America. To investigate a possible hypoglycaemic effect, concentrated aqueous extracts of cerasee were administered to normal and streptozotocin diabetic mice. In normal mice, intraperitoneal administration of cerasee improved glucose tolerance after 8 hr, and in streptozotocin diabetic mice the level of hyperglycaemia was reduced by 50% after 5 hr. Chronic oral administration of cerasee to normal mice for 13 days improved glucose tolerance. The cerasee extracts did not significantly alter plasma insulin concentrations, suggesting that cerasee may exert an extrapancreatic effect to promote glucose disposal.