The 5-methylcytosine (m5C) content of DNAs from Morris hepatomas of varying growth rates and from normal liver was analyzed. DNA methylation in all hepatomas studied was found to be 20-45% less than in normal liver. This result was confirmed independently by restriction endonuclease (Hpa II and Msp I) analysis. While these results agreed with recent literature data suggesting hypomethylation of DNA from some neoplastic sources, no correlation was observed between the extent of DNA hypomethylation and the growth rates of the tumors.