We have used a cDNA probe for mouse secreted phosphoprotein 1 (Spp-1, also known as 2ar, osteopontin, bone sialoprotein 1, 44-kDa bone phosphotein, tumor-secreted protein) to find a restriction fragment length polymorphism in the gene from C57BL/6J and DBA/2J mice. The strain distribution pattern in 25 BXD recombinant inbred lines is identical with that previously determined for the dominant, autosomal gene, Ricr (Rickettsia resistance). This places Spp-1 on mouse chromosome 5 with a 95% confidence limit of being within 4.32 cM of Ric. Evidence supporting the possibility of allelism between Spp-1 and Ric is briefly discussed.