To establish the time of onset of action and magnitude of response to the quickest disintegrating sublingual nitroglycerin tablet available in Scandinavia (Nitromex), nine patients with stable exercise-induced angina were studied whilst performing bicycle exercise tests. In the first session, placebo, 0.25, 0.50 and 0.75 mg sublingual nitroglycerin (Nitromex) was given in a double-blind cross-over fashion on different days. In the second session (1 h after Session 1), nitroglycerin 0.5 mg (Nitromex), placebo and 0.5 mg of a different brand of nitroglycerin were compared for the time of onset of attenuation of ST-segment depression when administered during exercise. In Session 1, there was a dose-dependent fall in systolic blood pressure and a concordant rise in heart rate whilst sitting at rest prior to exercise. Exercise time and ST-segment depression were dose-dependently prolonged, significantly by the two higher doses, (mean 20 and 26%, respectively) which did not differ from one another. In Session 2, nitroglycerin (Nitromex) caused ST-segment reversal after a mean of 123 s after administration, which was shorter than after ordinary nitroglycerin (mean 157 s) and placebo (two tests, 186 and 192 s). It is suggested that when nitroglycerin is administered during exercise, chest pain and ischaemic ECG-changes are largely improved through coronary vasodilatation and reduced afterload rather than through increased venous pooling and reduction in preload.