Apoptosis plays an important role in cancer pathogenesis. Several oncogenes and antioncogenes regulate this process. Loss of their normal function leading to cell resistance to apoptosis seems to be a key factor of neoplasm development. In tumour cells, programmed cell death is a spontaneous process and its intensity increases after chemo-, radio- and hormonotherapy. Amongst several genes and their products, bcl-2 and p21 genes play a significant role in the process. p21 gene product, cyclin-dependent kinase inhibitor, along with p53 gene take part in cell cycle regulation. Our study aimed at evaluating p21 and Bcl-2 protein expression in the cells of patients afflicted with stage IIIA of non-small cell lung cancer who underwent neoadjuvant chemotherapy (three courses of Vepesid and Cisplatin). Protein expression was evaluated in slides of tissue material obtained before pharmacological treatment (during bronchofiberoscopy) and after three courses of Vepesid and Cisplatin (during surgical tumour resection). Protein activity in tissue slides was conducted using histochemical method with labelled antibodies (immunoperoxidase staining procedure). The control material was obtained from patients who had not undergone inductive chemotherapy. The results were documented as photographs and presented as charts after extinction level measurement using cytophotometric technique. Decrease in Bcl-2 protein activity and increase in p21 protein level in tumour cells of patients after inductive chemotherapy were observed.