The aim of the study was to examine the effects of intensive insulin therapy using lispro on metabolic control, immunogenicity and beta-cell function of newly diagnosed type 1 diabetic subjects in comparison with intensive insulin therapy using regular insulin. An open study was conducted in 45 newly diagnosed type 1 diabetic subjects. Patients were randomly assigned to intensive insulin therapy using insulin lispro (lispro) (lispro, n=22; 22.8 years) or intensive insulin therapy using regular insulin (regular) (regular, n=23; 24.4 years): three to five injections of subcutaneous rapid-acting insulin before meals and Neutral Protamine Hagedorn (NPH) before dinner/bed-time. GAD, IA2, insulin antibodies, basal and stimulated plasma C-peptide and HbA(1c) were measured initially and at months 1, 4, 8 and 12. Daily blood glucose profiles tended to be lower in the lispro group, particularly values after breakfast, without reaching statistical significance. There were no differences in terms of HbA(1c) throughout the study. The proportion of subjects achieving an HbA(1c)<6% at the end of the study was similar in both groups (regular 73.9%, lispro 68.0%). The number of mild hypoglycemic episodes tended to be lower with lispro, but not significantly. beta-Cell function was not significantly different in both groups. During follow-up there were no differences in antibodies, including IAAb. In summary, insulin lispro used in intensive insulin therapy is as effective as regular insulin in optimizing metabolic control and preserving beta-cell function at diagnosis of type 1 diabetes.