['Elevated lipoprotein (Lp) (a) concentrations are associated with coronary artery disease and myocardial infarction. Lp(a) is structurally related to proteins involved in lipid transport, fibrinolysis, coagulation, and cellular mitogenesis and is known to have important physiological interactions with the coagulation and fibrinolytic systems. Because these processes may be important to arterial healing after balloon injury, we hypothesized that elevated Lp(a) concentrations may be associated with recurrence of symptoms and restenosis after balloon angioplasty.', 'We assessed 240 consecutive patients undergoing coronary balloon angioplasty with measurements of Lp(a), total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, apolipoprotein A-I, and apolipoprotein B-100 concentrations from fresh specimens. Patients were evaluated 4 to 6 months after angioplasty for clinical recurrence by repeat angiography if angina had returned or by maximal exercise treadmill testing with thallium imaging if patients remained asymptomatic. Ninety-seven patients (40%) had clinical recurrence; 143 (60%) did not. Patients with recurrence had significantly greater Lp(a) concentrations compared with those without (median, 29 versus 14; P < .0001). Each patient quintile stratified by increasing Lp(a) concentrations had incrementally greater recurrence rates ranging from 27% (lowest quintile) to 60% (highest quintile). By multivariate logistic regression analysis, Lp(a) concentration was the only predictor of recurrence (P < .0001). A subset of frozen, stored serum samples showed a significant decrease in measured Lp(a) concentration over time (mean, 605 days; P < .01).'] Is elevated serum lipoprotein ( a ) a risk factor for clinical recurrence after coronary balloon angioplasty?