The effect of karela (Momordica charantia), a fruit indigenous to South America and Asia, on glucose and insulin concentrations was studied in nine non-insulin-dependent diabetics and six non-diabetic laboratory rats. A water-soluble extract of the fruits significantly reduced blood glucose concentrations during a 50 g oral glucose tolerance test in the diabetics and after force-feeding in the rats. Fried karela fruits consumed as a daily supplement to the diet produced a small but significant improvement in glucose tolerance. Improvement in glucose tolerance was not associated with an increase in serum insulin responses. These results show that karela improves glucose tolerance in diabetes. Doctors supervising Asian diabetics should be aware of the fruit's hypoglycaemic properties.