Patients with stage IIIB or IV non-small cell lung cancer will be randomly allocated to receive: (a)PG regimen: paclitaxel 120 mg/sqm followed by gemcitabine 1,000 mg/sqm i.v. on days 1 & 8 q 3 weeks; (b)GA regimen: gemcitabine 1,250 mg/sqm i.v. on day 1 (plus folinic acid 350 μg daily orally and vitamin B12 1,000 μg i.m. q 9 weeks), pemetrexed (Alimta®) 500 mg/sqm i.v. on day 8 followed by gemcitabine 1,250 mg/sqm, q 3 weeks.