Insulin availability following the addition of whole blood to insulin infusions was evaluated. Solutions of 0.45% sodium chloride containing insulin (50) units/liter) and tracer amounts of 125I-labeled insulin were prepared and added to plastic or glass intravenous containers. Blood (5 ml) was added to the containers at the same time as the insulin or one hour after insulin. The cumulative amount of insulin delivered from these solutions over six hours was compared with that of insulin solutions containing no blood. When no blood was added to the insulin infusions, cumulative insulin delivery after two hours was 68% from the plastic containers and 76% from the glass bottles. The corresponding values for blood added simultaneously with insulin or one hour after insulin, ranged between 93% and 98%. The addition of whole blood to these low-dose insulin intravenous infusions was found to be effective in minimizing insulin adsorption onto the components of the infusion system. The method described does not expose the patient to the risks associated with receiving exogenous human serum albumin and also involves less expense.