Fish scales are calcified by calcium phosphate like bones and teeth. In fish, scales function as a calcium storage organ like bones in mammals. Since scales are located on the surface of the body, they are dealt easily for experiments, and therefore they are thought to be a good model for calcium phosphate calcification study. Goldfish scales were decalcified with an EDTA solution, and the extract was purified by reverse-phase HPLC to afford two separate fractions: one with calcification-promoting activity and the other with calcification inhibitory activity. From the former fraction, a glycoprotein named GSP-21 was isolated and identified, while from the latter fraction highly phosphorylated protein named GSP-37 was isolated and identified. The reason for the promotion activity of GSP-21 was not clear. A strong calcification inhibitory activity of GSP-37 was due to post-translational phosphorylation at many Ser/Thr residues. A cDNA encoding GSP-37 was cloned, and recombinant GSP-37 was prepared by E. coli expression system. In situ hybridization and immunohistochemistry using antiserum raised against the recombinant GSP-37 identified GSP-37 producing cells in the calcified area of scale, suggesting that GSP-37 plays a role in calcification. Unfortunately, a homologous gene of GSP-37 was not found in human genome.