This invention relates to NPH-insulin (crystalline preparations) that are prepared in the presence of certain high-affinity ligands for the HisB10 Zn.sup.2+-sites of the R-state insulin hexamer. Preparation of NPH-insulin in the presence of high-affinity ligand results in crystalline NPH-insulin suspensions that are absorbed more slowly from subcutis than regular NPH-insulin. Hence the resulting action profile is longer and the spike is less pronounced than observed with regular NPH-insulin