Plasma lipids, lipoproteins, and apolipoproteins were assessed in three groups of Nigerians at increased risk for atherosclerotic heart disease. The three patient groups, diabetes mellitus (n = 15), essential hypertension (n = 12), and hypertensive-diabetes mellitus (n = 11), were compared with age-matched, apparently healthy controls (n = 14). In subjects with diabetes mellitus, triglyceride and its related apolipoproteins CIII and CIII:NonB were significantly higher than controls. High-density lipoprotein cholesterol (HDL-C) was significantly lower; its related ratios, total/HDL-C and low-density lipoprotein cholesterol (LDL-C)/HDL-C were significantly higher than those for controls. Subjects with hypertension and hypertensive-diabetes mellitus had significantly higher values than controls for those lipids and lipid fractions considered atherogenic (total cholesterol, LDL-C, triglyceride, and the total/HDL-C and LDL-C/HDL-C ratios) as well as apolipoproteins B, CIII, and lipoprotein particles Lp(a) and CIII:NonB. Only hypertensive-diabetes mellitus subjects had lower HDL-C levels, while hypertension patients had significantly higher apolipoprotein AI and LpAI concentrations than controls. Subjects with hypertensive-diabetes mellitus had significantly worse lipid, lipoprotein, and apolipoprotein profiles both in terms of increased atherogenic and reduced anti-atherogenic parameters compared with subjects with diabetes mellitus or hypertension only. These studies suggest that Nigerians with diabetes, hypertension, and especially both hypertension and diabetes need to be fully evaluated from a lipid and lipoprotein standpoint, and any abnormalities detected need to be taken into consideration during therapy of this group of high-risk patients.