To assess the value of serum interleukin (IL) 10 levels as an immunological marker in atopy and to determine the role of an IL-10RA gene single nucleotide polymorphism (SNP) (serine 138-to-glycine exchange [S138G]) in the pathogenesis of atopic diseases.Seventy-five patients with atopic disorders were compared with 25 age-matched healthy volunteers. Serum total immunoglobulin (Ig) E and IL-10 levels were measured by enzyme-linked immunosorbent assay and the IL-10RA gene S138G variant was screened by multiplex allele-specific polymerase chain reaction.There was a significant association between G allele frequencies of the S138G variant (62%, 60% and 68% for atopic asthma, atopic dermatitis, and allergic rhinitis, respectively) in atopic patients compared to in controls. There were significant differences in mean IgE levels but not mean serum IL-10 levels between the allelic variants in atopy groups.The IL-10RA gene SNP S138G may contribute to susceptibility to atopic diseases but serum IL-10 level is not a sensitive indicator in atopy.