Inclusion Criteria:

- Males and females with histologically confirmed NSCLC

- Prior treatment with a platinum- or taxane containing regimen

- Stage IIIB with malignant effusion, stage IV or recurrent NSCLC that is not amenable
to curative therapy (either surgery or radiation therapy)

- Measurable disease according to Response Criteria for Solid Tumors (RECIST)

- ECOG performance status of 0 or 1

- Life expectancy ≥3 months

- Adequate organ and marrow function

- No other malignancies within 5 years

- Signed informed consent

Exclusion Criteria:

- Radiation to ≥25% of bone marrow within 30 days of XL999 treatment

- Use of any systemic anticancer therapy within 30 days of XL999 treatment

- More than 2 prior systemic cytotoxic chemotherapy regimens

- More than 1 prior agent targeted against VEGF or EGFR (eg, bevacizumab, erlotinib, or
gefitinib)

- Subject has not recovered to ≤ grade 1 or to within 10% of baseline from adverse
events due to other medications administered >30 days before study enrollment

- Uncontrolled and/or intercurrent illness

- History of or known brain metastases, current spinal cord compression, or
carcinomatous meningitis

- Pregnant or breastfeeding females

- Known HIV