Late changes in the expression of oncogenes and tumor suppressor genes following carcinogenic exposure were examined in lung, liver and kidney. 1-Nitropyrene (1-NP), which is a high-risk exposure factor in urban and industrial zones, was used as a carcinogenic agent. c-myc, Ha-ras and p53 gene expression was investigated after administration of a single dose of 1-NP to sensitive CBA/Ca mice in lung, liver and kidney for one year. One week after a single dose 1-NP administration, the expression of p53 was elevated in the liver, but, decreased in the lung and kidney. There was no increase in the expression of c-myc or Ha-ras genes at that time. One month after the administration of the 1-NP, the expression of p53 was increased in the kidney while the expression of Ha-ras and p53 was elevated in the liver. There was no significant difference in gene expression between the treated and control animal groups at any of the investigated periods except for the above-mentioned organs and at the end point of the investigation. According to the literature, 1-NP and its metabolites remain at high concentrations in the kidney, liver and lung. The concentration of the carcinogenic agent and the expression of the studied genes did not seem to correlate with each other in this experiment.