The purpose of this study is to determine if TLK286(Telcyta) is more effective than gefitinib (Iressa) in the treatment of non-small cell lung cancer.

Inclusion Criteria:

• Clinical diagnosis of non-small cell lung cancer
• Non-small cell lung cancer that is not curable with surgery, radiation, or combined modality chemoradiation
• Failed two prior chemotherapy regimens which must have included platinum
• Measurable disease

Exclusion Criteria:

• Treatment with more than two prior chemotherapy regimens
• History of bone marrow transplantation or stem cell support
• Pregnant or lactating women
• Known history of prior gefitinib therapy
• Known history of prior TLK286 therapy