Noncollagenous proteins, including bone morphogenetic protein (BMP), were extracted in 4 mol/l guanidinium hydrochloride (GuHCl) from the pulverized and HCl-demineralized matrix of reindeer, bovine, sheep and porcine bone. To remove water-soluble material, the GuHCl solution was dialyzed against water and water-insoluble material and re-dissolved in 4 mol/l GuHCl. Gelatin peptides were removed by extraction in 0.25 mol/l citrate buffer (pH 3.1). The yield consisted mostly of large complexes and protein molecules of molecular weight less than 35,000 daltons. Isoelectric focusing of the material showed three to four different protein molecules: three acidic and one neutral. Bone-forming activity was investigated by implanting 0.6–15.0 mg of partially purified protein preparation into the thigh muscles of BALB mice. Radio-logically detectable formation of new bone required 0.6 mg of reindeer BMP, 2.5 mg of bovine BMP, 5.1 mg of sheep BMP, and 8.0 mg of porcine BMP. A rough estimate of the area of the deposits showed that reindeer BMP had the highest bone formation activity, and porcine had the lowest. The formation of new bone was confirmed histologically. It is suggested that the differences in osteogenic activity are due to quantitative differences in BMP constituents or in the degree of complex formation in the protein preparations. Also immune and other defense mechanisms may generate differences in osteogenic response.