The primary objective of this study is to compare the 2-hour PPBG excursion following a standard test meal in insulin-requiring diabetic patients treated twice daily with human insulin mix 50/50, versus the 2-hour PPBG excursion in patients treated twice daily with insulin lispro mix 50/50.

Inclusion Criteria:

1. Men and women who have had either type 1 or type 2 diabetes (World Health Organization[WHO]classification)for at least 2 months and are between the ages of 18 and 70 (inclusive) at the signing of the informed consent.
2. Have been treated with commercially available human insulin mix 50/50 or human insulin mix 30/70 twice daily as the only pharmacological treatment for their diabetes for at least 2 months prior to entering the study.
3. Have an HbA1c between 1.1 and 1.7 times the upper limit of the normal reference rang(inclusive) as determined by a local laboratory within 2 weeks prior to or at Visit 1.
4. Have achieved compliance with their diets and insulin therapies as determined by the investigators and perform regular blood glucose monitoring.
5. Have given informed consent to participate in this study in accordance with local regulations.

Exclusion Criteria:

{1] Have used oral antidiabetic agents, including biguanides, sulfonylureas, glucosidase inhibitors, and insulin-sensitivity enhancers within 30 days prior to entry into the study.

[2] Receive a total daily dose of insulin >2 units/kg.

[3] Have had more than two episodes of severe hypoglycemia (defined as requiring assistance of another person due to disabling hypoglycemia) within 6 months prior to entry into the study.

[4] Have a body mass index >35 kg/m2.

[5] Have serum creatinine > the upper limit of normal (ULN), as determined by a local laboratory.