Effects of dietary iron deficiency on inductions of putative preneoplastic lesions and oxidative alterations in the livers of rats by a choline-deficient L-amino acid defined (CDAA) diet were examined. Male Fischer 344 rats, 4 weeks old, were used with a total experimental period of 16 weeks, consisting of 4-week pretreatment and 12-week treatment periods (periods A and B respectively). During period A, a choline-supplemented L-amino acid defined (CSAA) or an iron-deficient CSAA diet was administered, and the CDAA or an iron-deficient CDAA diet was fed in period B. Formation of 8-hydroxydeoxyguanosine (8OHdG), a DNA adduct generated by activated oxygen species, in DNA and lipid peroxidation in liver cell membranes were sequentially determined after the beginning of period B. At the end of the experiment, development of gamma-glutamyltransferase (GGT) and glutathione S-transferase placental form (GSTP) positive liver lesions were quantitatively analysed. In the animals fed the CDAA diet, formation of 8OHdG and lipid peroxidation increased with time, and GGT and GSTP positive liver lesions developed. Formation of 8OHdG, lipid peroxidation and the numbers of induced enzyme-altered liver lesions were all reduced in rats fed the iron-deficient CSAA diet in period A and/or the iron-deficient CDAA diet in period B. The present results indicate that iron plays an important role in induction of preneoplastic liver lesions in rats caused by exposure to the CDAA diet possibly in connection with its known catalytic role in generation of highly reactive activated oxygen species.