Type 2 diabetes is associated with abnormal lipoprotein levels and altered plasma concentrations of insulin, intact and 32, 33 split proinsulin. To investigate whether these are early features of the disease, we studied 36 normoglycaemic first-degree relatives of patients with Type 2 diabetes (13 European, 15 of Asian (Indian-subcontinent), and 8 of Afro-Caribbean origin) and 36 control subjects with no family history of diabetes. Relatives and controls were matched for age (mean +/- S.E. 33 +/- 2 vs 34 +/- 2 years), body mass index (23.7 +/- 0.5 vs 23.7 +/- 0.6 kg m-2), sex (17 M, 19 F) and ethnic origin. After an overnight fast, blood was sampled for measurement of serum lipids, plasma glucose and insulin, intact and 32, 33 split proinsulin by specific immunoradiometric assays. Relatives and controls had similar fasting concentrations of glucose (5.0 +/- 0.1 vs 4.9 +/- 0.1 mmol l-1), total cholesterol (4.51 +/- 0.13 vs 4.54 +/- 0.17 mmol l-1), HDL-cholesterol (1.21 +/- 0.06 vs 1.10 +/- 0.05 mmol l-1), LDL-cholesterol (2.84 +/- 0.14 vs 2.96 +/- 0.14 mmol l-1) and triglyceride (median (range) 0.78 (0.44-2.45) vs 0.83 (0.41-4.03) mmol l-1). Fasting levels of insulin (50.4 (18.9-174.0) vs 51.6 (10.0-118.0) pmol l-1, intact proinsulin (2.8 (0.1-15.0) vs 2.1 (0.6-6.4) pmol l-1 and 32, 33 split proinsulin (2.0(0-23.7) vs 1.6 (0.3-6.0) pmol l-1) were not significantly different between relatives and controls.(ABSTRACT TRUNCATED AT 250 WORDS)