A combined rapid acting-long acting insulin formulation has been developed wherein the pH of the rapid acting insulin is decreased so that the long acting glargine remains soluble when they are mixed together. In the preferred embodiment, this injectable basal bolus insulin is administered before breakfast, provides adequate bolus insulin levels to cover the meal, does not produce hypoglycemia after the meal and provides adequate basal insulin for 24 hours. Lunch and dinner can be covered by two bolus injections of a fast acting, or a rapid acting or a very rapid acting insulin. As a result, a patient using intensive insulin therapy should only inject three, rather than four, times a day. Experiments have been performed to demonstrate the importance of the addition of specific acids to hexameric insulin to enhance speed and amount of absorption and preserve bioactivity following dissociation into the monomeric form by addition of a chelator such as EDTA. As shown by the examples, the preferred acids are aspartic, glutamic and citric acid. These are added in addition to a chelator, preferably ethylenediaminetetraacetic acid (EDTA). The results show that the citric acid formulation was more effective at dropping the blood glucose rapidly than the identical rapid acting formulation prepared with HCl in swine. Charge masking by the polyacid appears to be responsible for rapid insulin absorption. EDTA was not effective when used with adipic acid, oxalic acid or HCl at hastening the absorption of insulin. These results confirm the results seen in clinical subjects and patients with diabetes treated with the rapid acting insulin in combination with citric acid and EDTA.