The integrity and biological activity of multidose, preserved formulation epoetin alfa stored in syringes at 2-8 degrees C were studied. Three independent 1.0-mL hubless syringes of epoetin alfa 20,000 units/mL were aseptically prepared and refrigerated for three and six weeks (a total of six syringes). Protein integrity was assayed by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblotting, and glycoprotein detection. Biological activity was determined through a cell-based proliferation assay. The presence or absence of microbial contamination was observed after a one-week culture. A multidose, preserved formulation of epoetin alfa that was opened only at the time of assay served as the reference standard. SDS-PAGE silver-stained gels and immunoblots demonstrated no evidence of erythropoietin degradation after three and six weeks of storage when compared with the reference standard. In addition, SDS-PAGE, immunoblotting, and direct glycoprotein detection found that protein glycosylation was unaffected by the storage. Student's t test detected no significant difference between stored samples and the reference standard in biological activity (p > 0.05). A culture of epoetin alfa in bacterial and eukaryotic cell growth media showed no evidence of contamination. The results suggest that epoetin alfa can be dispensed to patients in prefilled syringes every four to six weeks to coincide with their peritoneal dialysis schedule. The integrity and biological activity of 20,000 units/mL epoetin alfa in prefilled syringes remain intact after three and six weeks when stored at 2-8 degrees C.