Genomic clones spanning the human type I and type II interleukin-1 receptor loci have been isolated. Approximately 75 kb of genomic DNA is required to encode the type I receptor, and approximately 38 kb to encode the type II receptor. In each case, the receptor coding region is contained in only about 20 kb of DNA, with most of the rest of each locus representing the distance between the two (type II receptor) or three (type I receptor) presumptive promoters which drive transcription. The virtually identical location of introns within the ligand-binding portion of the coding regions reinforces the presumption that the two receptors derive from a common ancestor. Yeast artificial chromosomes (YACs) have been isolated which contain the two IL-1 receptors. One of the YACs also contains the T1/ST2 IL-1 receptor-related gene. The relative map position of these three genes has been determined.