Neovascularization is a critical component for the growth of tumors and is a dominant feature in diseases such as diabetic retinopathy and hemangiomas in infancy. Angiogenesis inhibition is a potentially important therapeutic modality. We have previously reported that AGM-1470 is a fungal-derived angiogenesis inhibitor that suppresses primary tumor growth and metastases and is also nontoxic. alpha-Interferon, an angiogenesis inhibitor, is effective in the treatment of life-threatening hemangiomas. We therefore attempted to treat murine primary tumors and metastases with a combination of AGM-1470 and alpha/beta-interferon. Treatment began after solid tumors formed. Six-week-old syngeneic C57BI/6 mice were treated for 21 days with either AGM-1470, or alpha/beta-interferon or AGM-1470 + alpha/beta-interferon. The combination of the angiogenesis inhibitors AGM-1470 and alpha/beta-interferon suppressed tumor growth by 80% compared with controls (P < or = .001). AGM-1470 and alpha/beta-interferon inhibited pulmonary metastatic tumor growth greater than sevenfold (P < or = .001) compared with controls. These effects were better than either inhibitor alone, and the combined effect was additive. Combination of angiogenesis inhibitors may be useful in the treatment of tumors and other angiogenesis-dependent diseases.