In an attempt to modify the cytotoxicity of cisplatin, amphotericin B (AmB) was given as pretreatment to BDIX rats with intracerebral BT4C glioma implants. Ten animals given AmB 5 mg/kg i.p. followed by cisplatin 5 mg/kg i.p. displayed massive haematuria within 24 h after treatment and died a few days later. The antitumoral effect could not, therefore, be evaluated. Histopathological examination of the kidneys showed extensive tubular necrosis. No signs of apoptotic cell death were found using in situ end labelling with biotin-labelled nucleotides or with DNA integrity analysis in agarose gel electrophoresis. An immunohistochemical method for analysis of cisplatin-DNA adducts was used to elucidate the distribution of cisplatin in brain tumour, normal brain and kidney. Addition of AmB to cisplatin caused increased adduct formation in kidneys, particularly in tubular cells. It seems plausible that the nephrotoxicity, at least in part, was mediated by increased levels of cisplatin-DNA adducts. Pretreatment with AmB did not have any obvious effect on the formation of adducts in the cerebral cortex. The adduct levels in the tumours from animals pretreated with AmB were not significantly increased compared with those treated with cisplatin only. Thus, addition of AmB to cisplatin caused excessive nephrotoxicity suggesting a decrease in the therapeutic ratio of cisplatin.