Abstract An investigation on the resolving power of hydroxyapatite columns is reported. The macromolecules chosen for this investigation have been five proteins endowed with a rigid structure and of different sizes: cytochrome c, lysozyme, β‐lactoglobulin A, collagen, and T2 phage. The following points have been investigated in detail: (1) the dependence of the elution molarity upon column length and slope of the gradient; (2) the dependence of the elution molarity and the width of the protein peak upon the load and the presence of other chromatographic components; (3) the optimal conditions for the resolution of macromolecules having the same size or different sizes.