Aberrant DNA methylation patterns are one of the earliest and most consistent hallmarks of cancer cells. Thus, the detection and classification of tumor-specific DNA methylation patterns provides a helpful tool for cancer diagnostics. We have established various biochemical and molecular methods for the identification and characterization of cytosine methylation patterns. Prominent examples include capillary electrophoresis for the determination of genomic cytosine methylation levels and RNA bisulfite sequencing for the analysis of RNA methylation patterns. These methods are now being used in a variety of projects. We are interested in characterizing methylation changes at microRNA genes and during cellular differentiation or aging. In addition, our methods are also being used for the characterization of drug-induced DNA methylation changes in cancer patients.