The recently described murine homeobox genes, Six1 and Six2, which are expressed during development in limb tendons, have also been shown to be expressed in skeletal and smooth muscle, respectively. We have cloned and sequenced a human SIX1 cDNA and shown by Northern blotting that it is expressed in adult skeletal muscle. The cDNA sequence and predicted protein sequence of SIX1 and Six1 are highly homologous, with 98% similarity over the entire predicted amino acid sequence. SIX1 was mapped to human chromosome 14 using a rodent/human somatic cell hybrid panel.