Low density lipoprotein (LDL) particle diameters were determined by non-denaturing gradient gel electrophoresis in 53 subjects with previously unrecognised coronary heart disease (CHD) and 167 control subjects matched by age, sex and total plasma cholesterol. The mean diameter of the major LDL peak was found not to be significantly different between the two groups, but the CHD subjects were found to have a broader distribution of the predominant LDL species ((25.0 (24.7-25.3)nm versus 24.8 (24.7-24.9)nm)) (median (25-75%)), a greater proportion of larger particles (chi 2 = 19.8, P < 0.001) and to be more likely to have multiple numbers of LDL species than the control subjects (chi 2 = 22.7, P < 0.001). A negative correlation was found between the diameter of the predominant LDL species and fasting plasma triglyceride (r = -0.21, P = 0.0015), waist to hip ratio (WHR) (r = -0.15, P = 0.026) and body mass index (BMI) (r = -0.20, P = 0.002), and in a subgroup of subjects (n = 106), postprandial analysis revealed a negative correlation with the incremental postprandial response of plasma insulin (r = -0.19, P = 0.025). Male subjects had a significantly smaller diameter of the major LDL peak (24.8 +/- 0.0 nm) than female subjects (25.0 +/- 0.0 nm, P < 0.001). The present study failed to confirm an association between small LDL particles and the presence of coronary heart disease but did demonstrate more LDL heterogeneity in those with CHD. In addition, significant relationships were evident between the diameter of the major LDL peak and a number of other risk factors for coronary disease.