Natural killer (NK) cells are innate immune-system lymphocytes capable of killing tumor cells. They secrete cytokines, including interferon (IFN)-γ, which participate in shaping the initial inflammatory and downstream adaptive immune responses. Its potent immunoregulatory action means that IFN-γ might be beneficial in cases of tumor rejection, but its severe side-effects limit clinical applications. This pilot study compared low-dose IFN-γ prepared by sequential-kinetic-activation (SKA), with standard-dose recombinant (r) IFN-γ, in terms of ex-vivo cytotoxic activity of peripheral blood (PB)-NK cells from colorectal carcinoma (CRC) patients. This was tested against the NK-sensitive K562 cell line and the less-sensitive human CRC Caco-2 and HT-29 cell lines. Twenty primitive non-metastatic CRC patients, five metastatic CRC patients, and thirteen healthy donors were enrolled. PB lymphocytes (PBL) were exposed to medium alone, SKA-IFN-γ (0.25fg/ml) or rIFN-γ (1ng/ml). NK-cell cytolytic activity was examined via short-term (51)Cr-release. Pretreatment of PBL from non-metastatic patients with SKA-IFN-γ caused a significant increase in NK-cell cytotoxicity, compared to those from normal donors, although less markedly than pretreatment with rIFN-γ against all three cell lines. In contrast, PBL from metastatic CRC patients displayed significantly decreased NK-cell activity and responsiveness to both rIFN-γ and SKA-IFN-γ treatments. These results demonstrate in principle the immunomodulatory capacity of low-dose SKA-IFN-γ, and might open the door to the possibility of generating a novel, safe, and feasible approach to enhancing NK-cell antitumor activity in early-stage CRC patients.