OBJECTIVE: To determine if the sterility of filgrastim (G-CSF) is maintained for up to 7 days when aseptically transferred from the vial to tuberculin syringes in a laminar air flow environment. DESIGN: The study was conducted in two phases: a validation and an experimental phase. The method was validated by inoculating samples of sterile filgrastim solution with common bacterial and fungal skin contaminants. Samples were aseptically drawn into syringes in a class 100 horizontal laminar air flow hood and refrigerated. The samples were equally divided and transferred to microbiology culture media at times 0, 24 hours, 48 hours, and 7 days; incubated; and the organisms identified and quantitated. In the experimental phase, samples of filgrastim were aseptically drown into syringes, separated into three groups, and refrigerated. At 24 hours, 48 hours, and 7 days, the samples were transferred to broth, incubated, and observed for the development of turbidity. SETTING: A class 100 laminar air flow hood in a pediatric hospital pharmacy and a home-infusion pharmacy class 100 000 clean room. MAIN OUTCOME MEASURES: The sterility of filgrastim in syringes was determined by comparing experimental broth culture tubes to a control tube and observing for the development of turbidity. RESULTS: Filgrastim demonstrated the ability to support the growth of intentionally inoculated skin contaminants, both qualitatively and quantitatively. However, when aseptically transferred to syringes and refrigerated, all tested filgrastim samples remained sterile for at least 7 days. CONCLUSIONS: Syringes of filgrastim remain sterile for 7 days when prepared in a class 100 laminar air flow hood, using aseptic, technique, and stored under refrigeration. This change in practice can result in significant cost savings.