Insulin-dependent diabetic patients with diabetic nephropathy have a highly increased morbidity and mortality from cardiovascular diseases. To determine whether altered levels of apolipoprotein(a) (apo(a)), the glycoprotein of the potentially atherogenic lipoprotein(a) (Lp(a)), contribute to the increased risk of ischaemic heart disease, apo(a) was determined in 50 insulin-dependent diabetic patients with diabetic nephropathy (group 1), in 50 insulin-dependent diabetic patients with microalbuminuria (group 2), in 50 insulin-dependent diabetic patients with normoalbuminuria (group 3), and in 50 healthy subjects (group 4). The groups were matched with regard to sex, age and body mass index. The diabetic groups were also matched with regard to diabetes duration. The level of apo(a) was approximately the same in the four groups, being: 122 (x/ divided by 4.2) U l-1, 63 (x/ divided by 4.4) U l-1, 128 (x/ divided by 3.5) U l-1 and 126 (x/ divided by 3.7) U l-1 (geometric mean (x/ divided by antilog SD)) in group 1, 2, 3 and 4, respectively. 1 U l-1 apo(a) approximates 0.7 mg l-1 Lp(a).(ABSTRACT TRUNCATED AT 250 WORDS)