Inclusion Criteria:

- Diagnosis of locally advanced or metastatic (Stage III or IV at entry) non-small cell
lung cancer (NSCLC) that is not amenable to curative therapy.

- Patients must have been previously treated with one platinum-containing chemotherapy
regimen for locally advanced or metastatic disease. Patients are also eligible if
they have received one platinum-based chemotherapy regimen as neoadjuvant or adjuvant
chemotherapy, but must have received an additional chemotherapy regimen upon
recurrence.

- No more than two prior systemic anti-cancer therapies will be allowed.

- Prior radiation therapy is allowed to less than 25% of the bone marrow. Prior
radiation to the whole pelvis is not allowed. Prior radiotherapy must be completed
at least 2 weeks before study enrollment, and the patient must have recovered from
the acute toxic effects of the treatment prior to study enrollment.

Exclusion Criteria:

- Pregnancy.

- Breast-feeding.

- Second primary malignancy that is clinically detectable at the time of consideration
for study enrollment.

- Inability to interrupt aspirin, or other nonsteroidal anti-inflammatory agents for a
5-day period.

- Inability or unwillingness to take folic acid or vitamin B12 supplementation.