Naturally occurring modulators of carcinogenesis, including dietary compounds, can either stimulate or inhibit cancer development. Mechanisms responsible for these effects are unknown. Garlics used in this study were freshly prepared, and their effectiveness in augmenting natural killer (NK) activity was evaluated. Administration of 20 mg/kg produced an optimum augmentation of NK activity. A glycoprotein with MW of about 14 kDa was isolated from garlic extract and its activity was assessed. It could induce NK augmentation against K562 tumor cell line. In vivo studies also confirmed that Fraction Residue 10 (R10) of garlic extract partially purified by ultra filtration and further purified by chromatography could induce a resistance to the growth of spontaneous mammary carcinoma in Balb/c mice. NK cytotoxic activities were evaluated by flowcytometry.