Pyrosequencing is a technique used to determine the percentage of DNA methylation in a sample. DNA methylation involves the addition of methyl groups to cytosine residues and is an epigenetic mechanism that regulates gene expression.

Pyrosequencing is performed on bisulfite-treated DNA. During the bisulfite treatment process, free cytosine residues are converted into uracils, while cytosine residues bound to a methyl group remain as cytosine. This allows subsequent sequencing to identify methylated cytosines and determine the methylation level (%) in a sample.