NOVELTY - Preparation of calcium salts of 3-hydroxy-3-methylbutyrate (I) its hydrate and/or solvate, involves: (1) preparation of a 3-hydroxy-3-methyl-butyric acid (II) by protonation of salt of 3-hydroxy-3-methyl-butyric acid compound (III) in presence of solvent (1) and acid (1); and (2) preparation of the compound (I) by deprotonation of the compound (II) in presence of solvent (2) and salt (2).    USE - For the preparation of calcium salts of 3-hydroxy-3-methylbutyrate (claimed); for reducing blood levels of total cholesterol; and in preparations for inhibiting protein depletion or as immuno-stimulating feedstuff additives for mammals.    ADVANTAGE - The process provides a solution. The reaction mixture is concentrated which allows high throughput production. The filtration of the product is rapid and easy. No excess of reagent is required; no hazardous reagents are used and the reagents are readily available. The reaction times are short in each of the process steps and the temperature ranges are close to room temperature. Each process step is highly selective, the basic medium of the method warranties no formation of pH dependent side products which further can degrade the starting material (DMA promotes the degradation of 4,4-dimethyloxetan-2-one into isobutene and carbon dioxide). The process is free of the use of hypochlorite or hypobromite, i.e. does not use a haloform reaction, no chloroform or bromoform is present, since chloroform is mutagenic and is anticipated to be a human carcinogen. The process gives a product with low value of 3,3-dimethylacrylic acid (DMA) and mesityl oxide (MoX), preferably DMA content of less than 12 ppm, and MoX content of less than 6 ppm.    DETAILED DESCRIPTION - Preparation of calcium salts of 3-hydroxy-3-methylbutyrate of formula (I) its hydrate and/or solvate, involves: (1) preparation of a 3-hydroxy-3-methyl-butyric acid (II) by protonation of a compound of formula (III) in the presence of a solvent (1) and an acid (1), where the solvent (1) is selected from water, acetonitrile, hexane, heptane, dichloromethane, dichloroethane, carbon tetrachloride, toluene, xylene, mesitylene, dioxane, 1-4C alkyl ether, tetrahydrofuran (THF), or 2-methyltetrahydrofuran, and the acid (1) is selected from polymeric sulfonic acid resin, aqueous HC1, HC1 gas, HBr, HI, HF, HCN, H2SO4, HNO3, HNO2, MsOH, TsOH, TfOH, BzOH, trifluoroacetic acid, ammonium chloride, or phosphoric acid; and (2) preparation of the compound (I) by deprotonation of the compound (II) in the presence of a solvent (2) and a salt (2), where the solvent (2) is selected from water, acetonitrile, ethanol, 2-methyl-1-propanol, isopropanol, MTBE, THF, acetone, or methanol, and the salt (2) is selected from CaCO3, Ca(HCO3)2, Ca(OTf)2, Ca(OMs)2, Ca(OTs)2, Ca(OBz)2, CaBr2, CaF2, CaI2, CaNO3, CaSO4, Ca(HSO4)2, Ca(OAc)2, Ca(O-aryl)2, Ca(O-16C alkyl), CaS, Ca(SH2), Ca3(PO4)2, Ca(HPO4), Ca(H2PO4)2, CaCl2, CaO, or Ca(OH)2.    m=1 or 2;    N=Na, Li, K, Ag, Cu, Ni, or Mg;    n=1 or 2.    Provided that: the compound (III) is not prepared by a haloform reaction from diacetone alcohol.