Differential scanning calorimetry has been used to investigate the heat of fusion (ΔH_f=7·12 kcal per g mol) and true melting temperature (T₀=422·4°K) of pure cholesterol (99·5 mole%). In addition to analysis of the thermograph by an existing method a new and more rapid procedure has been used for evaluation of the purity of substances. Evidence is given that differential scanning calorimetry measurements at low scanning rates (0·5,1° min⁻¹), followed by correction for premelting, are essential for estimation of ΔH_f of substances not ultra-pure, at higher scanning rates large errors result. The entropy of fusion of cholesterol is similar to that of the simpler cholesteryl esters.