A retrospective post-marketing surveillance of Transiderm-Nitro 5 was undertaken in 1803 general practice patients with various degrees of severity of angina. Over half the patients were assessed more than 3 months after starting treatment. At the time of assessment two-thirds of the patients were continuing with their Transiderm-Nitro therapy. Only a small proportion (3.8%) of the total patient population were withdrawn after 3 months' usage. This suggests the continuing benefit of longer term Transiderm-Nitro therapy. Subjective assessment of a reduction in the number of anginal attacks and an improvement in exercise capacity occurred, respectively, in 76.2% and 62.6% of the patients. Although 16% of patients experienced problems specifically related to patch use, only 6.4% withdrew for these reasons. The incidence of headache decreased with time of usage of Transiderm-Nitro to give an over-all withdrawal of 7%. The death rate observed during the surveillance lies between that for the United Kingdom population as a whole and that for a population with angina pectoris. This surveillance shows that both patients and doctors perceived clinical benefit from Transiderm-Nitro when used in the treatment of angina.