The association between lipoprotein and apolipoprotein levels and the degree of renal failure was investigated in 72 conservatively treated patients with chronic renal disease. The progression of renal insufficiency was attended by marked increases in total triglycerides, and very-low-density (VLDL), low-density (LDL) and high-density (HDL) lipoprotein triglycerides. Total cholesterol was slightly elevated due to a rise in VLDL cholesterol. There was no change in LDL cholesterol, whereas HDL cholesterol decreased. Apo C-II and C-III showed distinct increases, their mass ratio decreasing only insignificantly. Apo B and A-I were unaffected by the degree of renal insufficiency, whereas apo A-II decreased. The findings reflect compositional changes within HDL and the accumulation to triglyceride-rich lipoproteins in chronic renal disease. The alterations in the plasma lipoprotein pattern were demonstrable even in early stages of renal failure and, therefore, may bear a serious risk for the acceleration of atherosclerosis.