AbstractCapsicum frutescens has been used to treat diabetes mellitus by traditional healers in Jamaica. Purification experiments employing thin layer chromatography (TLC) and high performance liquid chromatography led to the extraction of the active principle, capsaicin. Purified capsaicin caused a decrease in blood glucose levels to 4.91 ± 0.52 (n = 6) mmol/dL versus 6.40 ± 0.13 mmol/dL (n = 6) for the control (p < 0.05) at 2.5 h in an OGTT in dogs. There was a concomitant elevation in plasma insulin levels (p < 0.05). In conclusion, it can be stated that capsaicin is the major constituent of Capsicum frutescens that is responsible for the hypoglycaemic episodes seen in the dogs. It is also apparent that the latter is mediated by insulin release. Copyright © 2004 John Wiley & Sons, Ltd.