A multicenter study was carried out in order to evaluate the efficacy and tolerability of 2 doses of a nitroglycerin transdermal system (TTS-NG 5 mg/24 h and TTS-NG 10 mg/24 h) on a large population of patients affected by angina pectoris. Nine hundred and seventy three cardiologists enrolled a total of 6,986 patients, 4,290 males and 2,696 females, mean age 61.7 years (range 26-95), 3,283 with effort-angina, 2,062 with mixed angina and 1,641 with angina at rest. Patients whose angina was not satisfactorily controlled by their previous therapy, were given TTS-NG 5 for 1 week in the morning, while continuing their antianginal treatment, with the exception of nitrates which were gradually withdrawn. At the end of this period, patients who responded to the treatment continued taking the same dose for a further 6 weeks, while poor responders were given a double dose of the study medication over the same period. Six thousand two hundred and sixty patients (90%) completed the study. TTS-NG 5 proved to be effective in 2,091 patients (33%) with a reduction in weekly anginal attacks after only 1 week of treatment (from 5.8 +/- 2.9 to 2.4 +/- 2.3). This reduction improved in the following 2 weeks (from 2.4 +/- 2.3 to 1.2 +/- 1.6) and subsequently remained virtually unchanged. Four thousand one hundred and sixty-nine patients (67%), whose angina was not sufficiently controlled by TTS-NG 5 (from 5.0 +/- 2.4 to 4.3 +/- 2.8), received double the dose at the end of the first week. TTS-NG 10 brought about a reduction in weekly anginal symptoms during the 2nd and the 3rd week (from 4.3 +/- 2.8 to 2.0 +/- 2.2), with a further decrease during the following 2 weeks (from 2.0 +/- 2.2 to 1.1 +/- 1.7). The reduction in anginal attacks was of the same extent both during the day and the night, thus suggesting that the drug is effective throughout 24 hours. A similar pattern was observed in the reduction of the number of anginal attacks weighted by their severity, the severity of attacks weighted by their number and the number of trinitrine pills taken. Tolerability was good in the majority of cases. In conclusion, this study confirms the efficacy of TTS-NG in the treatment of angina pectoris, thus supporting some recently published data obtained by using more standardized protocols and rigorous evaluation criteria.