Interleukin-10 (IL-10) is an important regulatory cytokine whose involvement extends into diverse areas of the human immune system. Recent characterization of the promoter and 5' flanking regions has demonstrated the presence of positive and negative regulatory segments in the promoter. In addition, the characterization of two dinucleotide repeat elements immediately upstream of the gene has shown that there is considerable polymorphism directly associated with the human IL10 gene. In the present report, we describe the mapping of the human IL10 gene to a discrete area of chromosome 1, the definition of a potential cytokine-responsive segment 3 - 4 kilobases upstream of the transcription initiation site, and the identification of two new point mutations in the immediate promoter region with their distribution in a panel of 75 unrelated healthy individuals. These data should further the understanding of how the IL10 gene is controlled in humans and how its function may vary between individuals.