Atopy is a growing problem for Korean children. Since eicosapentaenoic acid is a precursor of less active inflammatory eicosanoids, n-3 polyunsaturated fatty acids (PUFA) may have a protective effect on atopy. This study was undertaken to determine whether n-3 PUFA in red blood cells (RBC) is lower in atopic than in non-atopic preschoolers. Three hundred and eight Korean children aged 4-6 years were enrolled. Total RBC fatty acid composition was measured by gas chromatography. The prevalence of atopic dermatitis, allergic rhinitis, or asthma was 29%. Total RBC n-3 PUFA were lower in preschoolers with atopy than controls (9.8 +/- 1.2 vs. 11.4 +/- 1.6%; P<0.05), while n-6 PUFA (33.0 +/- 1.4 vs. 32.2 +/- 1.0%; P<0.05) and n-6/n-3 PUFA ratio (3.4 +/- 0.6 vs. 2.8 +/- 0.5; P<0.05) were greater. The following factors were also associated with an increase in atopy: higher saturated fatty acids (39.6 +/- 1.4 vs. 40.6 +/- 1.9; P<0.05) and arachidonic acid (15.3 +/- 1.6 vs. 16.0 +/- 2.9; P<0.05), and lower total PUFA (43.8 +/- 0.7 vs. 42.8 +/- 1.4; P<0.05) and omega-3 index (EPA + DHA; 9.1 +/- 0.8 vs. 7.8 +/- 0.5; P<0.05) in RBC. Maternal history of atopy was a significant (P<0.05) risk factor, while lactation was not. The results suggest that a reduced content of n-3 PUFA in the RBC membrane could play a role in early children atopy.