K-ras gene expression in the regenerating liver of the patial hepatectomy was tested by using dot hybridization. The K-ras gene transcription after the patial hepatectomy is amplified and its RNA splicing patern is changed. In normal liver exon 4a is spliced out and only K-ras proteins containing exon 4b are produced. In regenerating liver exon 4b is spliced out and K-ras proteins containing exon 4a might be produced at least 1000% more than in the normal liver.