We have described three physicians aged 65-70 years, who had noticed during their insulintherapy significant, periodically recurrent variations of insulin requirement (max. 50 i.u./24h vs 25 i.u./24h) in the periods of 4-16 weeks. They had been characterized by similar diet and physical activity, stable normal body mass (av. BMI 24.6) and normal glycosylated hemoglobin (av. HbA1c 5.9%). The hypothesis was put forward that the cause of this phenomenon may be periodical changes in the incretin system activity or increased proliferation of pancreatic beta cells leading to decrease of insulin requirement.