Lispro is a human insulin analogue with a very rapid onset of action, and a shorter duration of activity than soluble insulin. In order to assess the therapeutical value of lispro, we have had an open-label, non-comparative study, for 12 weeks, involving 19 IDDM patients. The treatment regimen with lispro and Humulin N has been adapted depending on each patient characteristics. Patients attended three visits, and the main metabolic control parameters included values of hemoglobin Alc, fasting and postprandial blood glucose monitoring. The patients themselves monitored their blood glucose using a glucometer. The mean age value of 19 patients (8 females and 11 males) was 22.32 (+/- 13.59) years. In patients previously receiving insulin treatment, therapy with lispro insulin significantly reduced postprandial glucose values. Lispro has been administered t.i.d. in 14 patients, and b.i.d. in 5 patients. At visit 1, mean value of HbAlc was 10.32% (+/- 1.63%); at visit 3, mean HbAlc was 9.90% (+/- 1.59%). Total insulin daily dose and the rate of short and long acting insulin did not change from visit 1 to visit 3. There has been reported only one serious adverse event during the study: a ketoacidosis due to a technical dosing error. Ten patients have reported mild hypoglycemic episodes. The outcomes of clinical study and of Quality of Life Questionnaire suggests that lispro--the first human insulin analogue used in humans--is effective, safe, and it is broadening beneficially the spectrum of insulins.