Several studies indicate that local immunoregulation and associated cytokines have a putative role in the development of cancer. There is evidence that pro-inflammatory cytokines such as interleukin-1 (IL-1) are critically involved with tumour progression. IL-1 receptor antagonist (IL-1Ra) is known to down-regulate and limit the inflammatory response. Therefore we attempted to examine the influence of the known polymorphism of the IL-1Ra gene on the development of human colorectal cancer (CRC). The study included 125 patients with CRC and 134 controls. Variable number tandem repeat (VNTR) polymorphism in intron 2 of the IL-Ra gene was analysed by the polymerase chain reaction method. There was a significant difference in genotype distribution between CRC patients and controls (P=0.025) and also in allelic frequencies (P=0.012). In detail the carriage rate of allele 3 in CRC patients was significantly increased compared with controls (P=0.007). We also found that the allelic distribution differs significantly between colon and rectum (P=0.041) and that allele 3 was overabundant in colon. The frequency of allele 1 in CRC patients with localized disease (Dukes A+B) was higher compared with disseminated disease (Dukes C+D), (P=0.035). These findings therefore suggest that the IL-1Ra polymorphism is associated with colorectal carcinogenesis.