A member of the ras gene family was identified here for the first time in two marine fish, the flounder (Platichthys flesus) and the red mullet (Mullus barbatus). After RT-PCR the partial sequence of ras gene (exons 1 and 2) has been cloned and sequenced from normal liver. At the nucleic acid level, a very high extent of homology with the human ras genes is observed (80% to 86%) and a perfect homology is observed at the amino acid level. The high conservation of the 5' region of the ras gene suggest that the p21 protein has identical function in higher and lower vertebrates. The identification of ras gene should be a first step in understanding the molecular basis of carcinogenesis in these species.