The major events comprising the de novo formation of calcium phosphate salts from buffered solutions were: (1) the initial deposition of amorphous calcium phosphate; (2) its subsequent transformation into small crystals of apatite; and (3) the ultimate growth or ripening of those crystals. The degree of metastability for any given calcifying solution was shown to be an exact function of pH, ionic strength, temperature, sol Ca P molar mixing ratio, and initial Ca × P millimolar product. Initial mineral-phase formation lag time was also sensitive to changes in solution viscosity and dielectric constant. The presence of pyrophosphate, fluoride, magnesium, carbonate, collagen, or gelatin always enhanced amorphous calcium phosphate formation, while addition of lysozyme, casein, phosvitin, poly- l-lysine, or protein-polysaccharides enhanced initial mineral-phase formation only at relatively low initial Ca × P millimolar products. Citrate, poly- l-glutamate, and polyacrylate always inhibited amorphous calcium phosphate formation, whereas chondroitin sulfate and protein-polysaccharides were inhibitory only at relatively high initial Ca × P millimolar products.