Improved understanding of the physiology and pharmacokinetics of insulin and new therapeutic devices allow an increasingly rational approach to the treatment of diabetes with insulin. The complexity of the regimen necessary for successful control of blood glucose levels depends largely on a patient's relative deficiency of endogenous insulin. Patients initially treated successfully with single or twice-a-day injections often, as the amount of endogenous insulin dwindles, progress to a complex regimen more closely mimicking normal patterns of secretion. Self-monitoring of blood glucose values and attention to many simple factors affecting absorption of insulin and glycemic behavior strongly enhance the success of all regimens. Patients and physicians must collaborate to plan and execute individualized therapeutic regimens using available tools to the best advantage.