Several reports suggest that CmCWGG methylation tends not to co-exist withmCG methylation in human cells. We have asked whether or not methylation at CCWGG sites can influence CG methylation. DNA from cells expressing an M.EcoRII-GFP fusion was actively methylated at CCWGG sites. CG methylation as measured by R.HpaII/R.MspI ratios was unchanged in cells expressing the transgene. Cloned representatives of CmCWGG methylated DNA often contained, or were adjacent to an ALU repeat, suggesting that M.EcoRII-GFP actively methylated gene-rich R-band DNA. The transgenic methyltransferase applied CmCWGG methylation to a representative human promoter that was heavily methylated at CG dinucleotides (the SERPINB5 promoter) and to a representative promoter that was essentially unmethylated at CG dinucleotides (the APC promoter). In each case, the CG methylation pattern remained in its original state, unchanged by the presence of neighboring CmCWGG sites. Q-PCR measurements showed that RNA expression from the APC gene was not significantly altered by the presence of CmCWGG in its promoter. Kinetic studies suggested that an adjacent CmCWGG methylation site influences neither the maintenance nor the de novo methylation activities of purified human Dnmt1. We conclude that CmCWGG methylation does not exert a significant effect on CG methylation in human kidney cells. © The Author 2005. Published by Oxford University Press. All rights reserved.