Increased anticardiolipin antibodies (acL) are often associated with arterial thrombosis in patients with autoimmune diseases. A mural thrombus at the site of percutaneous transluminal coronary angioplasty (PTCA) has been suggested as the initial cause for restenosis after primarily successful PTCA. In this study, IgM- and IgG-acL were determined in 65 men with coronary artery disease treated by PTCA; patients with infectious and autoimmune diseases were excluded from the study. Follow-up coronary angiography was performed 12 months after PTCA; restenosis was defined as greater than or equal to 50% reduction in diameter of the coronary vessel. The series comprised 2 groups: 34 patients (mean age 56 +/- 8 years) with (group A) and 31 (mean age 55 +/- 9 years) without (group B) restenosis. Medical history and laboratory findings were comparable in both groups. In patients with restenosis, IgM-acL were more often increased (9 of 34) than were those in patients without restenosis (2 of 31; p less than 0.05); IgG-acL values did not differ in both groups. Furthermore, there was no correlation between any vascular risk factors or laboratory findings, or both, with both IgM- and IgG-acL levels. Thus, IgM-acL appear to be independent indicators for an increased risk for restenosis after PTCA. Our observations suggest that an autoimmune mechanism may have a role in restenosis.