Two standard hospital pumps have been modified to provide bimodal insulin delivery for use as "open loop+ artificial beta cells. The units have been designed to deliver both a low infusion basal rate of insulin for glycemic control during a fasting state in diabetics and a high infusion rate in response to a meal challenge. The basal rate can be varied in steps of 0;2 milliliter per hour from roughly one to three milliliters per hour. The higher infusion rate can be 10 to 20 times the basal rate in steps of two milliliter per hour with an automatic return to the basal rate after a 1- to 99-minute programmable interval. The burst rate is initiated manually at the start of a meal. Displays and monitors are available to indicate the basal and high delivery rates and times. The units have been used for intravenous and intraperitoneal insulin delivery in animals and diabetic patients. There is an improvement in glycemic control and normalization of plasma-free insulin levels in juvenile-onset diabetics treated with this pulsed mode of insulin delivery. The variation in pumping rates provides flexibility in treatment of a variety of glycemic challenges.