DNA methylation levels were measured in a series of murine and human melanoma cell lines consisting of matched variants of low and high experimental metastatic capacity. The percentage of cytosine residues modified to 5-methylcytosine ranged between 2.13-3.92% in these lines. Ten cell lines were established in culture from individual lung tumor nodules produced in nude mice by i.v. injection of DX-3 human melanoma cells. Upon reinjection into groups of nude mice the individual lines manifested marked diversity for lung nodule formation (median number of pulmonary tumor nodules ranging from less than 10/group-greater than 100/group). DNA methylation levels in these lines were also heterogeneous (range 1.59 +/- 0.13 (SD)-4.04 +/- 0.15%) but no correlation was detected between methylation status of the genomic DNA and metastatic capacity.