Insulin therapy, a corner stone of the treatment of diabetes mellitus, both type 1 and type 2, has undergone substantial modification since the manufacture of the first insulin preparations 90 years ago up to the present time. Human insulins, such as neutral protamin Hagedorn (NPH) insulins, remain a major instrument of therapy of diabetes mellitus despite rapid developments in this field of knowledge and the wide availability of insulin analogs. When prescribing these preparations, the attending physician should be absolutely confident that the patient has a minimum background of knowledge and skills indispensable for efficacious and safe treatment. Such skills include the habit of mixing NPH insulin suspensions by 20-fold turning the vial or the cartridge upside-down or rolling them between the palms in order to ensure the uniform distribution of insulin in the suspension and its accurate dosing. The manufactures place from one to three glass or metal bullets inside the vials and cartridges for more homogeneous mixing of their contents. P. Kaiser et al. undertook the study of several pharmaceutical forms of NPH insulin manufactured by different companies to estimate the accuracy of dosing (variability of the insulin dose depending on the number of turns of the cartridge for homogeneous mixing). The insulin concentration in a single dose was measured by high-performance liquid chromatography. Marked variability of the insulin dose after less than ten (three or six) turns was documented for all cartridges with the exception of Insuman Basal insulin cartridges ("Sanofi"). It may be expected that the accuracy of dosing will not deteriorate using these cartridges owing to the presence in them of three heavy metal bullets even if the patient does not perform the necessary mixing procedure for one or another reason.