Serum lipid peroxides, lipids, blood pressure, body mass index, and dietary intake in 190 urban men were compared with 190 age-matched rural men. Significantly higher levels of lipid peroxides, serum cholesterol, low-density lipoprotein cholesterol, and triglycerides were seen in urban men, compared with rural men. In rural men, serum lipid peroxides were related negatively to age; the same was observed in the 70 + y age group in the urban population. All the lipid constituents were related positively to age in both populations. There were statistically significant correlations between lipid peroxides and serum cholesterol and triglycerides in the urban men. The marked elevation of lipid peroxides and lipids in urban men may be the result of urbanization, including exposure to environmental pollutants.