OBJECTIVE To examine the influence of the nephrotic syndrome on lipoprotein(a) [Lp(a)], a plasma lipoprotein associated with atherosclerotic cardiovascular disease independently of low-density lipoproteins. Factors that modulate plasma Lp(a) concentrations are poorly understood. METHODS A total of 62 patients: 47 with primary kidney disease and 15 with diabetic nephropathy. METHODS Lipoprotein(a) levels were determined by enzyme-linked immunosorbent assay. Because apo(a) phenotype has a significant effect on Lp(a) levels, apo(a) isoforms were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, Western blotting, and immunoblotting; the data were compared with a healthy control group. RESULTS Nephrotic patients had significantly higher Lp(a) levels (mean, +/- SE, 69 +/- 10 mg/dL; median, 46 mg/dL, < 0.01) compared with 91 healthy controls (mean, 18 +/- 2 mg/dL; median 9 mg/dL). Sixty percent of the patients and 18% of the controls had values greater than 30 mg/dL. Lipoprotein(a) levels correlated significantly with apolipoprotein B, serum cholesterol, and low-density lipoprotein cholesterol but showed no correlation with creatinine, albumin, or proteinuria. Within all apo(a) isoform classes, higher concentrations of Lp(a) were seen in the nephrotic patients compared with controls (P < 0.05). Finally, in nine patients with primary kidney disease and elevated Lp(a) levels, remission of the nephrotic syndrome was induced using immunosuppressive drugs and Lp(a) values decreased dramatically (pretreatment mean, 90 +/- 15 mg/dL versus remission mean, 31 +/- 8 mg/dL). A decrease in Lp(a) levels was also observed when patients with diabetic nephropathy progressed to end-stage renal disease (nephropathy mean, 56 +/- 11 mg/dL versus dialysis mean, 34 +/- 10 mg/dL; n = 7). CONCLUSIONS Most patients with the nephrotic syndrome have Lp(a) concentrations that are substantially elevated compared with controls of the same apo(a) isoform. Because Lp(a) concentrations are substantially reduced when remission of the nephrotic syndrome is induced, it is likely that the nephrotic syndrome results directly in elevation of Lp(a) by an as yet unknown mechanism. The high levels of Lp(a) in the nephrotic syndrome could cause glomerular injury as well as increase the risk for atherosclerosis and thrombotic events associated with this disorder.