BACKGROUND: Sublingual nitroglycerin (glyceryltrinitrate, GTN) capsules or isosorbide dinitrate (ISDN) spray are routinely used to treat anginal attacks and to vasodilate maximally the epicardial coronary arteries during coronary angiography. OBJECTIVE: To compare the coronary vasodilatory effects of GTN capsules and ISDN spray with those induced by intracoronary GTN using quantitative coronary angiography. DESIGN: 96 patients (79 men and 17 women; median age 59 years) were randomised to four groups to receive either a sublingual capsule containing 0.8 mg GTN or two puffs of spray delivering 0.8 mg ISDN, followed or preceded by an intracoronary bolus of 0.2 mg GTN used as reference for maximal vasodilatation. RESULTS: There was a significant increase in the mean diameter of coronary arteries in angiographically normal segments in patients who received either intracoronary GTN (groups 1 and 2) or ISDN spray (group 4) as a first application (group 1, 0.46 mm, + 17%, (baseline vessel diameter 100%), p < 0.001; group 2, 0.45 mm, + 13%, p < 0.001; group 4, 0.47 mm, + 13%, p < 0.05). Patients who received a sublingual GTN capsule as the first application mode (group 3) had no significant change in epicardial vessel diameter (0.10 mm, + 5%, p = 0.3). CONCLUSIONS: Sublingual ISDN spray may be more efficacious than sublingual GTN capsules in certain patients with anginal attacks. ISDN spray should be preferred over capsules in coronary angiographic procedures.