There is evidence that a variety of anticancer drugs exert their cytotoxic activity by a free-radical-mediated mechanism. These drugs include anthracyclines such as adriamycin, daunorubicin, 4-epi-adriblastin as well as bleomycin, procarbazine, vincristin, cyclophosphamide, etoposide and mitomycin C. The aim of this study was to investigate whether cancer patients who underwent polychemotherapy (n = 44) show more signs of oxidative stress in plasma than a group of healthy controls (n = 52). As an index of free radical generation, plasma concentrations of thiobarbituric-acid-reactive substances (TBARS), well-accepted as markers for oxidative stress, were determined by fluorometric detection after separation by high-performance liquid chromatography. In 12 cases, the TBARS were measured both before and after a chemotherapy course. After chemotherapy, 10 of 12 patients showed a marked increase in plasma TBARS concentration compared to values measured before therapy [9.02 +/- 1.84 nmol/ml (n = 12) vs. 11.58 +/- 2.49 nmol/ml (n = 12); p = 0.002, t-test for paired observations]. Tumor patients in general had significantly larger amounts of TBARS in plasma in comparison with a control group [mean 11.88 +/- 3.51 nmol/ml (n = 44) vs. 7.51 +/- 2.14 nmol/ml (n = 52); p < 0.001, t test]. Our results are evidence that repetitive polychemotherapy with radical-generating compounds may exceed the antioxidative capacities of cancer patients and may lead to oxidative stress.