Background The purpose of the study was to investigate the relation of lipoprotein(a) and serum lipid parameters to restenosis after percutaneous transluminal coronary angioplasty (PTCA) and to assess the association of these same biochemical markers to coronary artery disease (CAD) in individuals with angiographically defined normal and diseased coronary arteries.Methods and Results Sixty-two patients with successful PTCA had follow-up angiography at 35+-10 weeks. Restenosis occurred in 21 male patients (46%) and 6 female patients (38%). Elevated apolipoprotein B (P<.01) and decreased high-density lipoprotein-2 cholesterol (P<.02) were found to be independently associated with restenosis after angioplasty, whereas lipoprotein(a) was not.Eighty-five patients undergoing PTCA were compared with 46 subjects who had no evidence of CAD on angiography. Elevated lipoprotein(a) (P<.001) and reduced apolipoprotein A1 to B ratio (P<.001) were found to be strong independent risk factors for the presence of CAD when adjustment was made for age (P<.005), male sex (P<.01), smoking (P<.005), and hypertension (P=.06).Conclusions Serum lipoprotein(a) levels are not associated with restenosis after PTCA, but elevated levels are strongly associated with CAD. Low-serum, high-density lipoprotein-2 cholesterol concentration and elevated apolipoprotein B concentration were found to be associated with restenosis after PTCA. (Circulation. 1994;89:1593-1598.)