The timing characteristics of appropriate mixtures of protamine zinc and regular insulin are well adapted to the needs in many cases of moderately severe to severe diabetes. Such mixtures provide the requisite intensity of insulin action during the day, when food is being ingested, and a prolonged action of low intensity for maintenance of control of diabetes overnight. An effective proportion in most instances is between 2 and 3 units of regular insulin to 1 unit of protamine zinc insulin. A fixed modification of protamine zinc insulin having an action like that of a 2:1 mixture of regular and protamine zinc insulin such as insulin type NHP 50, could be employed with satisfactory results in many more cases than the standard protamine zinc insulin which is now available. Its action could be further intensified and shortened by the addition of regular insulin when necessary.