Methylation of DNA in CpG dense regions of gene promoters (CpG islands) is important for transcriptional inactivation of selective genes in normal and neoplastic cells. Here, we present a spreadsheet-based program adapted from Microsoft Excel that is useful for identifying CpG islands and for assisting in the laboratory analysis of DNA methylation of these regions. Upon execution of the program, a customized workbook analyzes an entered DNA sequence for the total number and percentage cytosine and guanine nucleotides, the total number and percentage of CpG sites, and a CpG:GpC ratio. The program also displays the distribution of CpG sites in a visual format as well as in two different graphical formats. Finally, the program assists in laboratory studies of DNA methylation that employ bisulfite modification of DNA by displaying methylation-dependent effects of bisulfite treatment on DNA sequences.