An animal model was developed to investigate the expression of two oncogenes (c-myc, Ha-ras) and a suppressor gene (p53) as early markers of the effects of carcinogenic exposure and/or tumourigenesis. Inbred Long-Evans rats were treated with 7,12-dimethylbenz(a)anthracene and the transient/permanent gene expressions were measured after 24 and 48 hours by dot blotting in potential target tissues (lung, liver, lymph nodes, kidneys, spleen) and in peripheral blood leukocytes. The aim of the study was to test blood leukocytes, as surrogate tissue, showed similar expression patterns of the selected genes following carcinogenic exposure. c-myc did not prove to be an applicable early biomarker due to the lack of or low level of its expression. However, remarkable of early elevations were detected in the expression signals of Ha-ras and p53.