 This is a Phase 2, open-label, randomized, multicenter study of maintenance temozolomide versus observation in subjects with stable or responding stage IIIIV NSCLC to be conducted in conformance with Good Clinical Practices. Subjects will be randomly assigned to a study drug temozolomide or observation arm. The study drug will be administered at a dose of 75 mgm2 PO daily for 21 consecutive days, followed by a 7-day rest period, until progression or up to a maximum of 6 cycles, whichever occurs first. Subjects completing 6 cycles of treatment will be followed up for incidence of brain metastasis for up to 2 years, or until progression. 