The water-soluble scavengers ascorbic acid (Asc), cysteine (Cys), glutathione (GSH) and uric acid (UA) as well as DNA content were determined in 40 breast tissue samples (neoplastic and non-neoplastic tissues from 20 patients). To allow proper homogenization to take place, a fixed number of sections was cut from a tissue cylinder of known diameter. Adjacent sections were stained with hematoxylin-eosin and the fractions of epithelium, fat and connective tissue were estimated as a percentage of the section area. Protein-free extracts were injected into a reverse-phase high-pressure liquid chromatography system and scavengers quantified with 2 electrochemical detectors (gold and glassy carbon). DNA and all scavengers, except UA, were greatly increased in cancer tissues in nearly all cases. Amounts of Asc and GSH in neo plastic tissue correlated closely with DNA values and percentage of epithelium, those of Cys not so closely and those of UA not at all. We assume that Asc and GSH were located mainly in the epithelium, UA mainly in the extracellular space and Cys in both spaces. When values were expressed as μmol/g DNA, a parameter related to content per cell, values were higher in neoplastic than in non-neoplastic tissue for Asc (18/ 20 cases), GSH (17/20) and Cys (14/20) and lower in neoplastic tissue for UA (19/20). It is known that increased GSH protects cells against certain drugs in tissue cultures. For in vivo treatment the presence of increased Asc (and to a lesser extent Cys) in addition to GSH could be of importance.