The stability of pentamidine isethionate in small-volume intravenous admixtures was studied. In an initial experiment, duplicate admixtures containing pentamidine 1 or 2 mg/mL were prepared using 100 mL each of 5% dextrose injection and 0.9% sodium chloride injection in polyvinyl chloride (PVC) bags. All solutions were kept at room temperature and were assayed at various times up to 48 hours by high-performance liquid chromatography. Solutions were also examined visually and tested for pH at each assay time. In a second experiment, single admixtures containing pentamidine 2 mg/mL were prepared in 100-mL PVC bags of both 5% dextrose injection and 0.9% sodium chloride injection. After time-zero determinations of pentamidine concentration, pH, and visual clarity, solutions were allowed to run through PVC infusion sets at 20 mL/hr. Samples were collected at the distal end of each set at various times up to five hours for analysis of pentamidine concentration, pH, and clarity. All admixtures in the initial experiment retained greater than 90% of initial concentration for the 48-hour study period. However, 5% dextrose admixtures infused through PVC administration sets showed a loss in initial concentration of about 2%, while 0.9% sodium chloride admixtures lost about 10% of initial concentration after infusion through these sets. The pH of all solutions in both experiments varied by less than 0.5 units, and no particulate matter or color change was noted in any of the admixtures. In the concentrations and diluents studied, pentamidine appears to be stable for 48 hours in PVC bags. Slight losses in the initial concentrations of these solutions after infusing them through PVC infusion sets may be caused by adsorption to the set.