Nonhistone chromosomal proteins (NHCP) from normal, regenerating rat liver, fetal liver, stages during acetylamino-fluorene (AAF) and diethylnitrosamine (DEN) induced carcinogenesis, and resultant primary hepatocellular carcinomas (PHC) were analyzed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). These studies sought to determine if changes in proteins putatively involved in catalyzing specific gene expression (NHCP) occur during liver cancer development that might be related to the malignant phenotype. NHCP extracted in high salt-urea buffers, analyzed by 2D-PAGE and silver staining were resolved into some 530–560 polypeptides. Increases in number of NHCP amounting to 8.4, 8.6 and 8.8%, respectively, were detected in AAF induced nodules (AAF-NOD), AAF-PHCs and DEN-PHCs when compared to normal chromatins. The majority of the 51 qualitative changes detected reflected cell cycling and/or reexpression of fetal-NHCP. Within the total changes, seven new NHCP were found only in AAF- and DEN-induced PHCs. Further, four NHCP with isoelectric points and relative molecular weights (pI/MW) of 5.62/19.3, 5.96/30.7, 6.25/46.6 and 8.16/53.5 occurring in both AAF- and DEN-PHC also were found in AAF-NOD, a carcinogenesis stage considered to represent premalignant nodules. Reciprocally, three NHCP of pI/mol.wt.: 6.81/34.0, 5.82/43.7 and 8.18/67.0 present in normal liver, disappeared in all carcinogen involved tissues analyzed. These findings indicate that while AAF and DEN exposure results in a number of qualitative NHCP changes specific for the particular carcinogen, a total of only ten changes, seven inductions and three losses, occurred in common during hepatocarcinogenesis induced by these diverse agents. At least four of these NHCP may prove critical inductions during malignant conversion or alternatively might serve as tumor markers since they appear first in a well characterized premalignant stage and persist in resultant tumors.