We identified a CpG island at the 5' end of murine leukemia inhibitory factor gene (LIF). The CpG island is 0.6 kb long and covers most of the first exon and first intron. The region is non-methylated, its G+C content is 65% and relative frequency of CpG dinucleotide is 0.7. The block of 150 nucleotides, which is 72% conserved between murine, human, ovine and porcine genes, is a part of the CpG island. Two DNA fragments from this CpG island interact with nuclear proteins from NIH 3T3 cells. One fragment partially covers the block of conserved nucleotides. Human, ovine and porcine LIF genes also contain G+C- and CpG-rich sequences in the corresponding region.