The effects of cicletanine hydrochloride on glucose tolerance parameters were studied in a two-phase trial in which patients received a placebo for 2 weeks, followed by cicletanine 50 mg/day for 3 months. Ten patients with mild to moderate hypertension, who were neither obese nor diabetic and had no disorder of glucose tolerance entered the study. None of the patients was withdrawn. Glucose tolerance was evaluated by two oral glucose tolerance tests performed at 90 days’ interval, each with half hourly blood glucose and insulin assays. The clinical effectiveness of the drug was assessed by monthly blood pressure measurements. No significant change in glycaemia and insulinaemia was observed. There was a significant decrease of supine SBP from 170.7 +/- 9.1 mmHg to 150.3 +/- 6.7 mmHg (p less than 0.0001) and of supine DBP from 101.3 +/- 4.1 to 80.3 +/- 7.7 mmHg (p less than 0.0001). At the end of the study, 9 of the 10 patients had normal blood pressure values. No undesirable clinical or biochemical effect was noted. thus, cicletanine, an antihypertensive drug derived from furopyridine, proved to be devoid of adverse effects on glycoregulation and clinically effective on hypertension.