Preliminary results of a randomized study (radiotherapy versus radiotherapy plus weekly low-dose cisplatin) are reported. Fifty-four patients (43 evaluable) with stage IIIa-b non small cell lung cancer were randomized. Objective responses (CR + PR) were seen in 62% of the radiotherapy-treated group and in 63% of the group treated with radiotherapy plus cisplatin. No major toxicity was seen. Patient compliance for both treatments was satisfactory.