Dentinogenesis imperfecta type II (DGI1) is an autosomal dominant disorder of dentin formation, which has been mapped to human chromosome 4q12-q21. The region most likely to contain the DGI1 locus is a 3.2-cM region surrounding the osteopontin (SPP1) locus. Recently, a novel dentin-specific acidic phosphoprotein (dmp1) has been cloned in the rat and mapped to mouse chromosome 5q21. In the current investigation, we have isolated a cosmid containing the human DMP1 gene. The isolation of a short tandem repeat polymorphism at this locus has allowed us to map the DMP1 locus to human chromosome 4q21 and demonstrate that it is tightly linked to DGI1 in two families (Zmax = 11.01, theta = 0.001). The creation of a yeast artificial chromosome contig around SPP1 has further allowed us to demonstrate that DMP1 is located within 150 kb of the bone sialoprotein and 490 kb of the SPP1 loci, respectively. DMP1 is therefore a strong candidate for the DGI1 locus.