Abstract: Antibodies, humanized antibodies, resurfaced antibodies, antibody fragments, derivatized antibodies, and conjugates of these molecules with cytotoxic agents, which specifically bind to and inhibit insulin-like growth factor-I receptor, antagonize the effects of IGF-I and are substantially devoid of agonist activity toward the insulin-like growth factor-I receptor. These molecules can be conjugated to cytotoxic agents for use in the treatment of tumors that express elevated levels of IGF-I receptor, such as breast cancer, colon cancer, lung cancer, ovarian carcinoma, synovial sarcoma, prostate cancer and pancreatic cancer. These molecules can also be labeled for in vitro and in vivo diagnostic uses, such as in the diagnosis and imaging of tumors that express elevated levels of IGF-I receptor.