Studies in our laboratories have demonstrated that some herbal extracts exert hypoglycaemic effects via unclear mechanism(s). Since the extracts did not have any significant effects on plasma insulin concentration, we speculated that they interfered with food intake and/or absorption to reduce blood glucose concentration. Accordingly, we monitored the amounts of food consumed and body weights in separate groups of non-diabetic and streptozotocin (STZ)-diabetic rats orally treated with Tapinanthus nyasicus, Solanum incanum, Aloe chabaudii, Morus alba, Ficus thoningii and Allium sativum 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). Positive control groups of rats were administered standard allopathic hypoglycaemic drugs, metformin (50 mg.100 g−1 body weight) or glibenclamide (5 μg.100 g−1 body weight). The herbal extracts and standard drugs decreased blood glucose in a similar manner in non-diabetic and diabetic rats. Glibenclamide increased serum insulin concentration in non-diabetic rats whilst extracts and metformin did not have any affect. T. nyasicus leaf, F. thoningii bark, S. incanum fruit, and M. alba leaf extracts decreased weekly food consumption throughout the experimental period. Although S. incanum root or A. sativum bulb extracts increased food consumption, this was associated with high prevalence of diarrhoea and reduced weight gain. Glibenclamide and metformin decreased food intake in non-diabetic and STZ-diabetic rats; however, body weight gain was only reduced by metformin. The reduction of weight is of clinical significance, since this may check obesity often observed in type-2 diabetic patients. Most existing antidiabetic agents are associated with weight gain with the exception of metformin. Therefore, the hypoglycaemic effects of the herbal extracts probably mimic those of metformin as evidenced by similar effects on serum insulin concentration and weight changes. We conclude that herbal extracts examined produced hypoglycemia by partly interfering with either food intake or gastrointestinal glucose absorption.