1 The effects of transdermal nitrate (TN) (Transiderm-Nitro TIS, Geigy Pharmaceuticals, one 10 cm2 patch daily) and oral isosorbide dinitrate (ISDN) (Sorbitrate, Stuart Pharmaceuticals, 10 mg three times daily) were compared in a group of 20 patients with chronic stable angina pectoris. 2 Treadmill exercise duration was prolonged from a median time of 365 s to 428 s after ISDN (P < 0.05), but was unchanged after TN. The difference between the active treatments was not significant. 3 Weekly consumption of glyceryl trinitrate (GTN) increased during treatment with TN from a median value of 5.5 to 6.3 (P < 0.05). A decrease was observed after ISDN (7.8 to 3.9, P = NS), and the difference between the drugs was significant (P < 0.01). 4 Systolic arterial pressure was significantly lower during the ISDN than during the TN treatment period in both the supine (135 + 5 vs 128 + 5 mm Hg; P < 0.05) and standing positions (134 + 5 vs 122 + 5 mm Hg; P < 0.05). 5 No change in weekly attack rate, the degree of ST depression at angina on treadmill testing, or the number of episodes of ST depression recorded during a 24 h period by Holter monitoring was observed after either drug. 6 In this study, an antianginal effect was demonstrated for ISDN but not for TN. It is suggested that the dose of TN may have been inadequate to demonstrate such an effect, and further studies using a higher dose schedule will be required.