A human homologue of the recently cloned murine leukemia-inhibitory factor (LIF) gene was isolated from a genomic library by using the murine cDNA as a hybridization probe. The nucleotide sequence of the human gene indicated that human LIF has 78% amino acid sequence identity with murine LIF, with no insertions or deletions, and that the region of the human gene encoding the mature protein has one intervening sequence. After oligonucleotide-mediated mutagenesis, the mature protein-coding region of the LIF gene was introduced into the yeast expression vector YEpsec1. Yeast cells transformed with the resulting recombinant could be induced with galactose to produce high levels of a factor that induced the differentiation of murine M1 leukemic cells in a manner analogous to murine LIF. This factor competed with 125I-labeled native murine LIF for binding to specific cellular receptors on murine cells, compatible with a high degree of structural similarity between the murine and human factors.