Following reconstitution of Nallpen piggyback units with sterile water for injection or 0.9% sodium chloride, soln containing 10-20 mg of nafcillin per ml are stable for 72 hr @ room temperature or 14 days when refrigerated @ 2-8 °C. Following reconstitution of Nafcil piggyback units with sterile water for injection or 0.9% sodium chloride, soln containing 10-200 mg/ml are stable for 24 hr @ room temperature or 7 days when refrigerated @ 2-8 °C. Nallpen pharmacy bulk packages of the drug that have been reconstituted with sterile water for injection or 0.9% sodium chloride to a concn of 100 mg/ml are stable for 1 hr @ room temperature or 72 hr when refrigerated @ 2-8 °C; Unipen pharmacy bulk packages that have been likewise reconstituted are stable for 8 hr @ room temperature or 48 hr @ 2-8 °C. Nafcil pharmacy bulk packages that have been reconstituted with sterile water for injection or 0.9% sodium chloride to a concn of 250 mg/ml are stable for 72 hr @ room temperature or 7 days when refrigerated @ 2-8 °C or frozen @ -20 to -10 °C; at concn of 10-200 mg/ml, these soln are stable for 24 hr @ room temperature or 7 days @ 2-8 °C. When reconstituted as directed in 0.9% sodium chloride or 5% dextrose, nafcillin sodium soln prepared from Unipen ADD-Vantage vials are stable for 24 hr @ room temperature.