To characterize lipoprotein metabolism during early renal insufficiency, plasma lipid and apolipoprotein profiles were determined in normotriglyceridaemic (NTG, n = 31) and hypertriglyceridaemic (HTG, n = 30) middle-aged patients with primary renal disease and with moderately impaired renal function (GFR 20-55 ml/min, mean: 37.2). Mean GFR was similar in the two patient groups. They were compared with 102 normolipidaemic control subjects. In comparison with controls the NTG patients (plasma triglycerides TG < or = 1.7 mmol/l, mean TG: 1.16 mmol/l) had significantly increased plasma concentrations of apo C-III and apoB. The apoA-I levels tended to be lower and as a consequence the apoA-I/apoC-III ratio, considered to represent the hallmark of the altered apolipoprotein profile in renal dyslipoproteinaemia, was markedly lower in NTG patients (8.7 versus 16.8, P < 0.001). There was also a reduction of the antiatherogenic ratio apoA-I/apoB and an increase of the apoC-III/apoE ratio. The HTG patients (mean TG: 3.22 mmol/l) showed the same, but even more accentuated, qualitative changes as the NTG patients. There was a fourfold increase of apoC-III in VLDL-LDL lipoprotein fractions with little change in HDL in the HTG patients. In NTG patients the increase of apoC-III was found in VLDL-LDL and in HDL. Plasma insulin and PTH levels both correlated with the apoA-I/apoC-III ratio independently of GFR and BMI. This suggests a pathogenetic relationship between PTH-mediated alterations of insulin metabolism and the lipoprotein abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)