The availability of various dosages of insulin from a new collapsible polyolefin bottle fitted with a conventional polyvinyl chloride administration set was studied. Intravenous solutions containing various dosages of insulin (20, 40, 70, and 100 units), to which 125I-labeled insulin was added, were prepared. Solutions were mixed and delivered at a maintained flow rate of 125 ml/hour. Effluents were collected at 15, 30, 45, and 60 minutes and then at hourly intervals up to seven hours. One-milliliter samples were drawn from the end of the administration set at the end of each interval, and the level of radioactivity in the sample was measured. Greater percentages of binding occurred at the lower levels of insulin added. Saturation limits of 7.8, 2.7, and 5.4 units were found for the system, administration set, and bottle, respectively. Adsorption values for this bottle were less than that found in another study for polyvinyl chloride.