Nitroglycerin in sublingual, buccal and transdermal administration forms were compared in 10 patients with stable exercise-induced angina pectoris with respect to onset time of action and efficacy one and three hours after administration, using bicycle exercise to provoke chest pain. Anti-anginal and anti-ischaemic effects (as judged by influence on electrocardiographic ST depression) began within 2 minutes of application of the buccal and sublingual forms, whereas the transdermal patch did not show such effects within nine minutes of application. One and three hours after application, the sublingual form had no effect whereas both the transdermal and buccal forms significantly increased exercise capacity and improved electrocardiographic ST segment changes. The 2.5 mg buccal tablet was more effective than the 10 mg transdermal patch. An additional observation was that a light snack at 2 hours significantly decreased exercise capacity at 3 hours whether or not active treatment had been instituted.