The aim of this study was to investigate the effectiveness of immunomodulatory peptides in preventing the spontaneous onset of Type 1 diabetes in NOD mice. Two such peptides, CP and C1, were injected intraperitoneally in NOD mice three times a week starting at two different time points, nine weeks and 11weeks of age, and blood sugar levels monitored for the development of diabetes. CP was shown to be effective in delaying the onset of diabetes compared to control (P=0.006). The timing of peptide administration was crucial since delay in treatment did not prevent the onset of diabetes (nine weeks versus 11weeks of age). C1 was effective in delaying the onset of Type 1 diabetes with borderline significance when given at week 11 (P=0.05). These findings confirm the efficacy of these peptides in the prevention and possible treatment for Type 1 diabetes and thereby create new opportunities for genetic manipulation.