The outcome of a formulary interchange from filgrastim to sargramostim for the amelioration of neutropenia for outpatients receiving myelosuppressive chemotherapy was evaluated. The pharmacy department at the James Graham Brown Cancer Center of the University of Louisville Hospital implemented a therapeutic interchange program by following the Joint Commission on Accreditation of Healthcare Organizations performance methodology, incorporating four key elements: plan, do, check, and act. After the pharmacy and therapeutics committee agreed that filgrastim and sargramostim are therapeutically equivalent, the pharmacy initiated the interchange, with a commitment to collect outcomes data to analyze the impact of the program on patient outcomes. Inclusion criteria included patient age of > or = 18 years, the presence of solid tumors or lymphoma, and current treatment with traditional chemotherapy. Patient demographics and cycle-specific data were collected for 31 patients receiving sargramostim and 20 patients receiving filgrastim from August 2000 to July 2001. Absolute neutrophil counts (ANCs) were measured before initiating and after discontinuing colony-stimulating factors. The majority (70%) of all growth factor use was initiated within one to four days of the last chemotherapy dose. No appreciable difference was found between agents for median ANC at any measured time point. The majority of patients exceeded the target ANC of 1500 cells/mm3 at the time of growth factor discontinuation. There were no significant differences in the number of patients that had adverse effects or in the number of cycles resulting in an adverse event between groups. Sargramostim demonstrated a 21% cost savings over filgrastim ($1036 versus $1318, respectively). The formulary switch from filgrastim to sargramostim resulted in a significant cost savings for the institution without increasing incidence of adverse effects and negative outcomes associated with growth factor use.