Citrullinated peptides produced by enzymatic deimination of arginine residues in proteins by peptidylarginine deiminases are of particular interest in the pathogenesis of rheumatoid arthritis (RA). One type of citrullinated protein - the cyclic citrullinated peptide - is the target of the anti-cyclic citrullinated peptide antibody, the most sensitive and specific autoantibody in RA. The peptidylarginine deiminase type 4 (PADI4) gene, which codes one of the PADI enzyme isotypes, has genetic variants that confer susceptibility to RA in Asian, but not in European populations.Genetic associations were examined in 214 Hungarian RA patients characterized for the presence of anti-CCP and rheumatoid factor. The patients were characterized for the existing haplotypes of the PADI4 gene (defined by the combinations of 4 exonic padi4_89: 163G/A, padi4_90: 245T/C, padi4_92: 335C/G, padi4_104: 349T/C and 2 intronic padi4_94: 17535226C/T and padi4_102: 17546809C/T variants) by the PCR-RFLP method.None of the PADI4 haplotypes was accumulated in RA patients. One new finding was that we also did not detect the accumulation of any haplotypes either in the anti-CCP or in the RF-positive subgroups of patients.The data presented here show that none of the naturally occurring haplotypes of the PADI4 gene conferred susceptibility to RA in an average group of Hungarian patients; this is in agreement with findings for other European populations. In addition, none of the functional PADI4 haplotypes were associated with the pathologic immune response, which was evidenced by the absence of accumulation of anti-CCP-positive subjects in the specific PADI4 haplotypes.