1. Investigations were carried out to determine whether aqueous extracts of Osbeckia octandra, Artocarpus heterophyllus and Bambusa vulgaris truly possess oral hypoglycaemic activity. 2. All three plant extracts significantly lowered the fasting blood glucose level and markedly improved glucose tolerance in Sprague-Dawley rats. 3. A maximum hypoglycaemic activity was observed at +3 hr with O. octandra and B. vulgaris; with A. heterophyllus a maximum effect was not observed even at +5 hr. 4. The hypoglycaemic activity of O. octandra was comparable with that of tolbutamide while that of A. heterophyllus or B. vulgaris was better than that of tolbutamide. 5. The magnitude of the hypoglycaemic effects varied with the dosage used and the time of storage (except with A. heterophyllus, whose activity did not change with storage even up to 3 days).