Compatibility and stability of labetalol hydrochloride when mixed with commonly used large-volume parenterals (LVPs) were tested. Labetalol hydrochloride injection was added to 11 LVPs at concentrations of 1.25, 2.50, and 3.75 mg/ml. After initial samples were obtained, the admixtures were divided equally and stored for 72 hours at 4 degrees C and 25 degrees C. The initial samples and aliquots withdrawn at 6, 24, and 72 hours were frozen until analysis. The initial and 72-hour samples were analyzed for drug concentration, pH, osmolarity, and visual changes. High-performance liquid chromatography (HPLC) was used for the assay, and the American Public Health Association color-testing procedure was used in evaluating color. In the admixture with 5% sodium bicarbonate injection, a white precipitate formed within six hours. At both storage temperatures, the drug concentration in all other LVP solutions was not appreciably different from the initial concentration. No additional HPLC peaks were noted, and no measurable change in pH or osmolarity occurred. No haze, precipitate, or color change occurred in the 10 admixtures. Labetalol hydrochloride was stable for 72 hours at 4 degrees C and 25 degrees C in all i.v. solutions studied except 5% sodium bicarbonate injection.