To better understand the role of these kinases in the abnormal proliferation of malignant cells, we examined basal and epidermal growth factor (EGF)-inducible mitogen-activated protein kinase (MAPK), p70S6k and p90rsk activities in spontaneous hepatocellular neoplasms (adenomas and carcinomas) from CBA-T6 mice and in L1 sarcoma tumours implanted in livers of BALB/c mice. This evidence concerns the gene RPS6KA1 and carcinoma.