Apolipoproteins in delipidated VLDL preparations from normal, diabetic, and non-diabetic hyperlipidaemic subjects were analysed by SDS-polyacrylamide gel electrophoresis, and by isoelectric focusing. On electrophoresis, diabetic VLDL contained more apolipoprotein E (17.3 +/- 7.3 (+/- SD) %, n = 54) than did VLDL from hyperlipidaemic (13.4 +/- 4.2%, n = 52; p less than 0.005) or normal (12.4 +/- 2.6%, n = 29; p less than 0.001) subjects. Apolipoprotein E excess was also seen when subgroups were characterized by apolipoprotein E phenotype. In diabetic patients of E3/E3 phenotype, apolipoprotein E was 16.4 +/- 6.0% (n = 25), compared with 12.9 +/- 2.5% in control subjects (n = 14; p = 0.008). Acidic isoforms were more common in 44 diabetic patients with E3/E3 phenotype; E3, E2, E1, and E1' as percentage of total E apolipoprotein were 58.3 +/- 7.6, 24.5 +/- 4.4, 13.7 +/- 4.5, and 3.8 +/- 4.3% respectively, compared with 63.5 +/- 10.4 (p = 0.034), 19.1 +/- 5.3 (p less than 0.001), 13.7 +/- 6.5 (NS), and 3.7 +/- 2.1% (NS) in 21 normal subjects. In 31 diabetic patients, of apolipoprotein E3/E3 phenotype, E3, E2, E1 and E1' were 60.2 +/- 7.3, 23.4 +/- 9.4, 11.1 +/- 4.1, and 5.4 +/- 3.7%, respectively, compared with 68.0 +/- 7.1 (p less than 0.001), 21.9 +/- 6.4 (NS), 6.3 +/- 3.9 (p less than 0.001), and 3.7 +/- 2.5 (p less than 0.05) % in 32 hyperlipidaemic patients. Diabetic patients of E3/E2 phenotype showed less apolipoprotein E3 than normal or hyperlipidaemic subjects, with a similar trend for apolipoprotein E4 in those of E4/E3 phenotype.(ABSTRACT TRUNCATED AT 250 WORDS)