Previous studies in our laboratories suggest that oral administration of some herbal extracts reduce blood glucose concentrations in rats, possibly by interfering with food consumption and/or gastrointestinal absorption of food. Accordingly, we monitored the amounts of food consumed and body weights in separate groups of nondiabetic and streptozotocin-treated diabetic rats, orally treated with some plant extracts (20 mg 100 g -1 body weight) daily for 5 weeks. Control animals were administered the vehicle, citrate buffer (0.1 ml 100 g -1 body weight). Separate groups of rats administered allopathic hypoglycemic drugs metformin (50 mg 100 g -1 body weight) or glibenclamide (5 microg 100 g -1 body weight) acted as positive control animals. After 5 weeks, blood glucose concentrations were reduced in all the groups. Tapinanthus nyasicus leaf, Ficus thoningii bark, Solanum incanum fruit, and Morus alba leaf extracts decreased weekly food consumption throughout the 5-week study period. Similar results were obtained for the groups treated with metformin or glibenclamide. However, food consumption was increased by S. incanum root, Aloe chabaudii leaf, or Allium sativum bulb extracts, and this was associated with high prevalence of diarrhea. The herbal extracts and metformin did not affect serum insulin concentration in nondiabetic rats, while glibenclamide increased serum insulin concentration. In conclusion, it may be inferred that the herbal extracts examined produced hypoglycemia, probably by interfering with either food intake or gastrointestinal glucose absorption (as reported for metformin). These findings merit long-term investigation.