Inclusion Criteria:

- Must sign Informed Consent

- Females and males aged 18 years and over.

- Confirmed stage IIIB (T4-pleural effusion) and IV NSCLC.

- Either complete response, partial response, or stable disease following at least 4
cycles (3 in the setting of intolerable toxicity) but no more than 6 cycles of
definitive front line, platinum-based, doublet chemotherapy.

- No prior EGFR therapy

- No newly diagnosed intracerebral metastases while receiving or after completing
chemotherapy

- At least 3 weeks (21 days) but no more than 4 weeks (28 days) since last dose of
chemotherapy

- Must be completely healed from previous major oncologic surgery

- Life expectancy of ≥ 8 weeks.

Exclusion Criteria:

- Known severe hypersensitivity to ZD1839 or any of the excipients of these products.

- Any evidence of clinically active interstitial lung disease (subjects with chronic,
stable, radiographic changes who are asymptomatic need not be excluded).

- Other co-existing malignancies or malignancies diagnosed within the last 5 years with
the exception of basal cell carcinoma or cervical cancer in situ.

- Any unresolved chronic toxicity greater than common toxicity criteria (CTC) grade 2
from previous anticancer therapy excluding peripheral neuropathy or alopecia.

- Evidence of any significant clinical disorder or laboratory finding that makes it
undesirable for the subject to participate in the study.

- Pregnancy or breast feeding (women of child bearing potential). Women of
childbearing potential must practice acceptable methods of birth control to prevent
pregnancy.

- Treatment with a non-approved or investigational drug within 30 days before Day 1 of
study treatment.

- Signs of neurological symptoms consistent with new onset spinal cord compression or
CNS metastases.

- Treatment with any systemic anticancer therapies other than the prescribed protocol
chemotherapy regimen (refer to Inclusion criterion -). Exception: Palliative
radiotherapy for symptom relief of lesions present at diagnosis will be allowed;
however, this radiotherapy must occur prior to completion of pre-study doublet
chemotherapy.

- Males must also be willing to practice acceptable methods of birth control while
taking the drug to prevent pregnancy of a partner.