The biological activity of the multifunctional cytokine interleukin-1 (IL-1) is mediated by its receptors. The aim of this study was to determine if an association exists between single nucleotide polymorphisms (SNPs) in the IL-1 type 1 and 2 receptor genes (IL1R1 and IL1R2) and the expression level of membrane-bound IL1Rs on subpopulations of mononuclear cells or serum levels of soluble IL-1 receptors. It was observed that healthy individuals with the genotype TT in SNP rs2234650:C.T had a lower percentage of intact CD14 1 monocytes expressing IL1R1 on their surface. The SNP rs4141134:T.C in IL1R2 has also been associated with the percentage of intact CD3 1 T cells expressing IL1R2. Keywords: interleukin-1; membrane-bound receptor; SNPs; soluble receptor INTRODUCTION Interleukin-1 (IL-1) is a cytokine involved in a wide range of physiological processes, including having a central role in the regulation of acute and chronic inflammation. 1,2 The biological effects of IL-1 (IL-1a and IL-1b) are achieved by the binding of the cytokine to the membrane-bound IL-1 type 1 receptor (IL1R1). 3,4 IL1R1 is a glycoprotein with a molecular mass of 80 kDa that is predominantly expressed on endothelial cells, smooth muscle cells, epithelial cells, hepatocytes, fibroblasts, keratinocytes, epidermal dendritic cells and T lymphocytes. 5 IL-1 binding to the extracellular domain of IL1R1 promotes the recruitment of the IL-1 receptor accessory protein, which leads to signal transduction mediated by the cytoplasmic domains of IL1R1 and IL1R2 receptors. 6 The IL-1 type 2 receptor (IL1R2) is unable to initiate signaling and only acts as a 'decoy' receptor. 3,7 IL1R2 is a glycoprotein with a molecular mass of 60 kDa that is expressed on monocytes, neutrophils, T and B lymphocytes. 8,9 Studies have also provided evidence for the existence of soluble receptors for