Factors affecting the loss of diazepam from i.v. admixtures to flexible polyvinyl chloride (PVC) bags and to various administration sets were studied. Admixtures containing diazepam and 0.9% sodium chloride injection were stored for up to 550 hours in flexible PVC bags and in glass vials at various temperatures. Diazepam injection containing two different solvents was used. Initial diazepam concentrations in storage studies ranged from 25 to 100 micrograms/ml and pH ranged from 4.2 to 7.5. To determine availability of diazepam after infusion through administration sets, solutions (50 micrograms/ml) from glass containers were run through six different sets at 1 ml/min for seven hours. In storage studies, the difference in composition of the solvent was found to have only a slight effect on the rate and extent of diazepam loss. Diazepam loss was unaffected by pH. For admixtures stored in 1000-ml flexible PVC bags, the fractional loss of diazepam was greater at small volumes. The diazepam concentration of solutions in flexible PVC bags decreased more rapidly during infusion than during storage of the total original volume. The fraction of diazepam remaining in stored solutions was independent of the initial concentration, but the rate and extent of diazepam loss was greater at higher temperatures. Diazepam loss was dependent on length of flexible PVC tubing, and diazepam availability was greater with faster flow rates. In solutions infused through the polyolefin Tridilset, 100% of the diazepam remained. When storage of diazepam admixtures in PVC bags or administration through PVC tubing cannot be avoided, measures to minimize the rate and extent of diazepam loss include decreasing the temperature and the storage time and increasing the surface-area-to-volume ratio and the flow rate. Equations are presented for calculating the amount of diazepam delivered.