The present study was carried out to determine the variation in reduced glutathione (GSH), glutathione-reductase (GSH-R), DNA and RNA contents between tumours and adjacent normal tissue surgically removed from patients with breast cancer. A highly significant increase in the content of these parameters was found in tumours compared with adjacent normal breast tissue. Such observations were also found in the whole-blood GSH, GSH-R and leukocyte DNA and RNA content of these patients compared with that of normal women. The present data may provide relevant information about the behaviour of DNA, RNA, GSH and GSH-R in breast tumours that may be valuable in the chemotherapeutic modalities and prognosis of such tumours.