OBJECTIVE Overexpression of the bcl-2 gene as a result of the t(14,18) translocation leads to neoplastic transformation by suppressing apoptosis. However, apoptotic cell death in response to chemotherapy has not been investigated. This study was planned with the aim to investigate the association between bcl-2 gene rearrangements and apoptotic changes during chemotherapy in patients with non-Hodgkin's lymphoma. METHODS Lymphocytes from 33 patients were collected before and during chemotherapy. Bcl-2 gene rearrangements were investigated by PCR. Apoptotic cell death was analyzed by enzyme immunoassay. RESULTS In 24 cases, mbr gene rearrangements were detected. Apoptosis was successfully induced by chemotherapy in 48% of patients. Two characteristic, clearly distinguishable apoptotic response patterns with transient peaks either following the first or the third course were observed. It was found that apoptosis rates measured after the first course exactly reflect the final response. No correlation was found between bcl-2 gene rearrangements and apoptosis. CONCLUSIONS Apoptotic cell death rates show transient changes during chemotherapy. Because the midterm response can be misleading, the apoptotic response should be evaluated following the first course of chemotherapy.