Feulgen reaction, first described by Robert Feulgen, is one of the most commonly used cytochemical methods for semiquantitative DNA determination in histological and cytological samples. It is very important to determine the exact amount and status of the DNA of the nucleus in order to make a diagnosis and treat malignant tumors. The key parameter in the precise measuring of DNA is the reproducibility of the Feulgen reaction. If the instructions for use are followed correctly, reproducibility is easily and reliably achieved by using quality reagents found in BioGnost’s Feulgen kit. BioGnost’s Feulgen kit contains an additional contrasting reagent for cytoplasmic staining which enables clearer viewing of stained DNA. Using contrasting reagent is not necessary during the staining protocol, but it provides better contrast to the stained DNA of the section.