Dimethylbenz[a]anthracene is a pluripotent carcinogenic chemical, which acts as an initiator by causing point mutations in certain oncogenes and tumor suppressor genes. Changes in their expression may be another possible area of investigation the carcinogenic effect of DMBA. Elevated expression of oncogenes was previously has been shown after treatment with carcinogenic compounds. In the present study, expression of c-myc, c-Ha-ras and p53 24 hours after a single dose treatment of DMBA in the spleen and in the liver of Long-Evans rats was investigated. Control animals were injected with the solvent corn oil only. We could not find any significant change on the transcriptional level of the investigated oncogenes in the liver. In the spleen, the overexpression of Ha-ras was 2-fold and c-myc was 3-fold higher in the DMBA-treated rats than in the corresponding control group. Since DMBA is a typical environmental carcinogen, the results of animal experiments may serve as a basis for application of gene expression investigations as a screening method in humans.