BACKGROUND: The effect of sublingual glyceryl trinitrate (GTN) on the claudication distance (CD) and maximum walking distance (MWD) of patients with intermittent claudication was assessed. METHODS: Inclusion criteria were: history of intermittent claudication; resting ankle : brachial pressure index (ABPI) of 1.00 or less; fall in ABPI of more than 0.1 following exercise; and patient not taking nitrates. In the first study 22 patients (median age 69 (range 60-73) years, 16 men, five diabetic, median resting ABPI 0.57 (range 0.1-0.64)) had their CD and MWD measured on a treadmill set at 3.2 km h-1 and 10 per cent gradient. They were then randomized to either GTN or placebo spray, and the distances were remeasured. The crossover portion of the study was then completed. In the second study 28 patients (median age 68 (range 45-84) years, 20 men, six diabetic, median resting ABPI 0.57 (range 0.13-0.98)) were randomized to either GTN or placebo and walked at their own pace along a flat corridor for 15 min. Following a rest of 15 min, the crossover portion of the study was completed. Statistical analysis was by the Wilcoxon matched pairs signed rank test. RESULTS: CONCLUSION: GTN can increase the MWD by 19 per cent when patients with intermittent claudication are walked on a treadmill and by 9 per cent when walking at their own pace on a flat gradient.