Intravenous gamma globulin (IVIg) is produced from a pool of precipitated IgG from over 3,000 healthy donors. IVIg was originally given to subjects with Igs deficiencies. Later on its beneficial effects on a diverse autoimmune clinical conditions were revealed. Based on large experimental studies in mice as well as limited clinical experience, we consider IVIg useful in preventing metastatic spread. In mice, the employment of IVIg reduced significantly metastatic spread of melanoma, carcinoma and sarcoma. The effect of IVIg was achieved following i.v. or s.c. administration at high dose (2 g/kg body weight) and at 100 times lower doses. The effect of IVIg on the prevention of metastases are diverse and achieved via enhancement of IL-12 secretion and increased NK activity as well as inhibition of matrix metalloproteinase-9 (MMP-9). The lack of serious side effects with the remarkable decrease in metastatic spread make IVIg a suitable adjuvant therapy in early and advanced cancer conditions.