Interleukin-10 (IL-10) is an important immunoregulatory cytokine. We searched for new sequence variations in the 5' flanking region of the IL-10 gene by denaturing high performance liquid chromatography. A 3996 bp region spanning position -3934 to +61 was amplified in 12 polymerase chain reaction (PCR) fragments and each fragment was screened for variations in 23 Italian individuals. The following eight sequence variations all consisting of single base pair substitutions were identified: -3533A/T, -2769A/G, -2739A/G, -2013A/G, -1349A/G, -1255C/T, -851A/G, -657A/G. The new polymorphisms were analysed in an additional panel of random Italian individuals. The same samples were also tested for the IL10.G and IL10.R microsatellites, and for the two previously described single nucleotide polymorphisms (SNPs) at positions -1082 and -592. Highly significant pairwise linkage disequilibria were observed between alleles at most SNPs. Three major haplotypic combinations of alleles at multiple SNP sites were observed.