The short- and long-term effects of various Nitro-Dur formulations on performance and hemodynamics were studied in 15 men with stable angina pectoris who also had a positive treadmill exercise test. A treadmill exercise score (TES) was used that quantified the "ischemic" ST segment response to exercise. The score incorporated information that reflected the rapidity of evolution of ST segment depression during exercise and the time required for it to resolve after cessation of exercise. In early tests (n = 10) Nitro-Dur improved both the TES (by 31%: p less than 0.0001) and the time required for 1 mm ST segment depression (by 33%: p less than 0.0001). At all dosage levels, Nitro-Dur also decreased resting systolic blood pressure and increased resting heart rate. No dose-response patterns emerged. Changes in TES and time to ST segment depression were greater with sublingual nitroglycerin than they were with Nitro-Dur. In tests conducted after prolonged dosage (n = 5), the effects of Nitro-Dur on blood pressure and heart rate became attenuated at weeks 2 and 4, although cardiac responsiveness was preserved, as reflected in the increased time required before the occurrence of 1 mm ST segment depression. The latter effect was also observed with sublingual nitroglycerin. The clinical relevance of these data to the design of individual patient therapy is discussed.