An injectable formulation containing a rapid acting insulin and a long acting insulin has been developed. The pH of the rapid acting insulin is adjusted so that the long acting insulin, remains soluble when they are mixed together. Preferably, the formulation is administered before breakfast, provides adequate bolus insulin levels to cover the meal and basal insulin for up to 24 hours, and does not produce hypoglycemia after the meal. Lunch and dinner can be covered by two bolus injections of a fast, rapid, or very rapid acting insulin. Alternatively, by adjusting the ratio of rapid to long acting insulin, the long acting insulin may be shortened to a 12 hour formulation, and re-administered to the patient at dinner time, providing a safe and effective basal insulin level until morning. As a result, a patient using intensive insulin therapy should only inject three times a day.