We have isolated and characterized a cDNA clone encoding human homologue of senescence marker protein-30 (SMP30), a calcium binding protein also called regucalcin (RC). This clone (pHSMP6) has 1356 base pairs (bp) and contains an open reading frame of 897 bp, which encodes 299 amino acids. The estimated molecular weight of the deduced polypeptide is 33,250 and pI is 5.836. The homology of amino acid sequences between human homologue and rat SMP30 is 88.6%. Using pHSMP6 as a probe, the chromosomal location of the human homologue of SMP30 gene was determined. The results of regional mapping using a panel of 11 rodent-human somatic hybrids indicated that the gene is located in the p11.3-q11.2 segment of the X chromosome. This gene thus could be a candidate for one of the X-linked diseases mapped to this regions.