To investigate whether the high prevalence of coronary heart disease (CHD) and type II diabetes prevalent in Northern Mexico could be related to the presence at a young age of biomarkers for chronic disease, 25 boys and 29 girls (8-12 y old) from a low socioeconomic group were recruited. Plasma lipids, LDL phenotype, apolipoproteins (apos), glucose, and insulin were evaluated. Analysis of 3-d dietary records indicated the typical intake of this region to be high in total fat (37-43% energy) and saturated fat (11-13% energy). Boys and girls had an average of 6623 +/- 2892 and 6112 +/- 2793 steps/d, respectively, as measured by a pedometer, suggesting a low level of activity. Plasma total and LDL cholesterol (LDL-C) were within the 50th percentile. In contrast, the study population was characterized by having high triglycerides (TG) (95th percentile, 1.25 +/- 0.37 mmol/L in boys and 1.19 +/- 0.38 mmol/L in girls). HDL cholesterol (HDL-C) concentrations were low (25th percentile), 1.22 +/- 0.20 mmol/L in girls and 1.29 +/- 0.20 mmol/L in boys. There was also a high prevalence of the small dense LDL phenotype B (69%), which is associated with increased risk for CHD. These results suggest that the population of children studied may have 2 different components of risk, one being the high-fat diet, which could be associated with the elevated levels of plasma LDL-C present in the adult population. A second component, related to the insulin resistance syndrome, may be principally genetic and associated with the high TG, low HDL, and LDL phenotype B observed in these Mexican children.