The stability of milrinone and digoxin, furosemide, procainamide hydrochloride, propranolol hydrochloride, quinidine gluconate, or verapamil hydrochloride in 5% dextrose injection containing milrinone was studied. Milrinone admixtures with digoxin, furosemide, propranolol hydrochloride, quinidine gluconate, and verapamil hydrochloride were studied at two concentrations. Admixtures of milrinone and procainamide hydrochloride were studied at four concentrations. Duplicate solutions of each admixture and each control were prepared and stored in glass containers for four hours at room temperature (22-23 degrees C), under normal fluorescent lights. The samples were analyzed immediately by visual inspection, tested for pH, and assayed by high-performance liquid chromatography (HPLC). Milrinone 0.35 mg/mL-furosemide 4 mg/mL and milrinone 0.1 mg/mL-furosemide 5 mg/mL admixtures precipitated immediately after preparation and were not studied by HPLC. No changes in pH or visual appearance were observed in the remaining admixtures after storage at room temperature for four hours. Admixtures containing milrinone 0.175 or 0.2 mg/mL and procainamide hydrochloride 1, 2, or 4 mg/mL satisfied the USP standard for procainamide hydrochloride injection USP assay after one hour but failed this test in all cases after four hours. No degradation of milrinone was observed in any of the admixtures containing procainamide hydrochloride. Milrinone and furosemide are incompatible in 5% dextrose injection and should be administered separately. The remaining admixtures were compatible, and all except those containing procainamide hydrochloride were stable for four hours at room temperature.