Aim of this study was to define the optimal schedule of gemcitabine (GCB)\cisplatin (CDDP) combination as induction chemotherapy (CHT) in patients with stage IIIa pN2-IIIb non - small-cell lung cancer (NSCLC). Fifty patients with mediastinoscopically-proven stage-IIIa pN2 -IIIb NSCLC were treated with 3 cycles of induction CHT followed by surgery (if staged IIIa) and three-time-daily accelerated radiotherapy. Chemotherapy initially consisted of 3 courses of CDDP 100 mg\m(2) d1 plus GCB 1000 mg\m(2) dd 1,8,15 repeated every 4 weeks, than was modified in CDDP 80 mg\m(2) d1 plus GCB 1250 mg\m(2) dd 1,8 repeated every 3 weeks. Twenty-nine four-week scheduled treatment cycles were firstly administered to 10 patients (pts): treatment-related toxicity, mainly hematological, caused a dose-reduction or treatment omission on day 15 in 65% of cycles. After the protocol was amended, 119 three-week scheduled treatment cycles were administered to 40 pts. Treatment-related toxicity of the new schedule caused a dose-reduction or treatment omission in only 10% of cycles, no patients requiring chemotherapy discontinuation. Thirty-seven out of fifty patients (74%, 95% CI: 60-85%) achieved a partial response, 7 had stable disease and 6 had disease progression. Similar activity was seen with both schedules. One nodal pathological complete remission was observed among the 24 pts who underwent surgery. At present, with a median follow-up of 13 months (mos), 2-year (y) survival of all the 50 pts and of the 24 pts staged IIIa who underwent surgery is estimated as 37% (95% CI: 24-58%) and 47% (95%CI: 27-80%), respectively. When given as induction chemotherapy, a three-week schedule of CDDP plus GCB combination appeared to be effective, with lower toxicity and better compliance than a four-week schedule.