The purpose of this study is to compare the efficacy of ZD6474 and ZD1839 in patients with NSCLC after Failure of Prior Platinum-based Chemotherapy.

Inclusion Criteria:

• Failure of either first-line and/or second-line chemotherapy either of which was platinum-based (the prior regimen must have failed the subject because of toxicity or progression of tumor
• Prior histologic or cytologic confirmation of locally advanced or metastatic (IIIB/IV) NSCLC

Exclusion Criteria:

• Subjects who have received second-line or subsequent chemotherapy
• Any evidence of clinically active interstitial lung disease (patients with chronic, stable, radiographic changes who are asymptomatic, need not be excluded)