An in-vivo model has been developed to study early expressions of c-myc, Ha-rasoncogenes andp53suppressor gene as biomarkers of carcinogenic exposure and/or tumorigenesis. In order to validate the in-vivo expression changes as biomarkers, rats were treated with the outdoor air pollutant carcinogen 1-nitropyrene. The gene expression levels were measured after 24 and 48 h in potential target tissues (lung, liver, lymph nodes, kidneys, spleen) and in peripheral blood leukocytes. Another main objective was to prove the applicability of leukocytes as a surrogate tissue, having a similar expression pattern of the selected genes upon carcinogenic exposure. The c-myconcogene was not suitable as an early biomarker because of the lack or low level of its expression. However, in the case of the other oncogene Ha-rasand the suppressor genep53, remarkable and early changes were detected in the expression signals. Similar expression patterns could only be detected in leukocytes and the spleen; therefore we continue this validation study by using other types and routes of exposure.