Southern hybridization using 32P-labelled human interleukin 2 (IL2) cDNA probes revealed the existence of a single human IL2 gene. Five clones containing the human IL2 chromosomal gene were isolated from two different human DNA libraries cloned in either lambda Charon 4A or L47 phages. Analysis of the clones showed that they contained different, overlapping portions of human DNA which were derived from the same chromosomal segment. Restriction fragments which hybridized with labelled IL2 cDNA probes were subcloned into plasmid pUR250 and the sequence and organization of the IL2 gene was determined. It contains three introns, 90 bp, +/- 2400 bp and +/- 1900 bp in length, respectively. The organization of the genomic clone resembles that of another lymphokine, interferon-gamma, but no clear homology was found by comparing either the coding sequence or the 5'- and 3'-flanking sequences of the two genes.