Coccinia indica is a creeper which grows wildly in Bangladesh and in many parts of the Indian sub-continent. The plant has been used since ancient times as an antidiabetic drug by physicians who practice the Indian system of medicine known as Ayurvedha. We have conducted a double blind control trial with preparation from the leaves of the plant on uncontrolled, maturity onset diabetics. The trial lasted for six weeks for an individual patient. Out of the 16 patients who received the experimental preparations 10 showed marked improvement in their glucose tolerance while none out of the 16 patients in the dummy group showed such a marked improvement. This difference is highly significant (kappa 2 with Yates' correction = 11.7, P < 0.001).