The purpose of the current study was to assess the effects and safety of administering perioperative recombinant human granulocyte colony-stimulating factor (r-metHuG-CSF, Filgrastim; Roche, Switzerland) to patients undergoing elective colorectal surgery. Thirty consecutive patients were prospectively randomized to receive either r-metHuG-CSF or placebo. Treatment with r-metHuG-CSF induced transient leukocytosis with shift to the left. The phagocytic or killing capacities of neutrophils were not altered in the patients treated with r-metHuG-CSF, but there was a decline in neutrophil chemotaxis. There were no serious adverse events associated with r-metHuG-CSF treatment. Thus, perioperative r-metHuG-CSF is safe for patients undergoing colorectal surgery. The presence of an increased number of functioning neutrophils may offer advantages in combating imminent infection.