We conducted a randomised single centre double blind cross over clinical trial to investigate the effects of a herbal tea containing Salacia reticulata (Kothala Himbutu tea) in patients with type II diabetes mellitus. Fifty-one patients with type II diabetes mellitus for longer than 6 months and with evidence of stable glycaemic control over the preceding 6 months (as assessed by HbA1C) participated in the study. They were randomised to receive a standard preparation of Kothala Himbutu tea for 3 months followed by placebo in similar tea bags for a further 3 months (n = 28) or in reverse order (n = 23). All patients received detailed advice on diet, exercise and lifestyle modification. HbA1C was measured at recruitment, at 3 months and on completion of the study at 6 months. Liver and renal functions were assessed biochemically at baseline, at 3 and 6 months and adverse events were recorded. There were no significant differences between the two groups in age, body mass index, male/female ratio, glycaemic control and baseline laboratory tests. All patients completed both arms of the trial. The HbA1C at the end of drug treatment was significantly lower than after treatment with placebo (6.29 +/- S.D. 1.02 versus 6.65 +/- S.D. 1.04; P = 0.008). A statistically significant fall in HBA1c was seen with the active drug compared to a rise in HbA1C with the placebo group (0. 54 +/- S.D. 0.93) versus -0.3 +/-S.D. 1.05; P < 0.001. The daily mean dose of Glibenclamide fell by 1.89 (S.D. 6.2) mg in the drug treated group but rose by 2.25 mg in the placebo treated group (P = 0.07). The differences in the metformin dose were not significantly significant in the two groups. We conclude that Kothala Himbutu tea is an effective and safe treatment for type 2 diabetes.