The incidence of coronary artery spasm at the site of previous successful angioplasty and its importance in leading to subsequent restenosis or recurrence of symptoms are unknown. Fourteen consecutive patients with single vessel coronary artery disease who had undergone successful percutaneous transluminal angioplasty were studied. All patients were given ergometrine maleate (ergonovine maleate) intravenously during repeat cardiac catheterisation six weeks to three months after angioplasty. Five patients demonstrated excessive luminal reduction (spasm) at the site of previous angioplasty that led to luminal stenoses ranging from 50% to 79%. Two of these patients developed chest pain and ST segment changes during ergometrine maleate provocation and they also showed maximal vasoconstriction. The remaining nine patients did not develop important luminal change at the site of angioplasty after ergometrine maleate. Ergometrine maleate administration resulted in less than or equal to 20% reduction in lumen diameter of adjacent apparently normal sections of the coronary arteries in all but two patients. At the site of previous angioplasty in the five patients with spasm, however, the lumen was constricted by a mean (SD) of 51 (12)%, whereas in the nine patients not demonstrating spasm mean reduction was 12 (7)%. Thus hypersensitivity to ergometrine maleate at the site of previous successful angioplasty was demonstrated in over a third of consecutive patients with single vessel coronary artery disease. The importance of this finding to long term results of coronary angioplasty needs to be investigated further.