Preferentially, DNA should be extracted from fresh or frozen tissue as this will be of the highest quality, though it is now possible to use archival material which is formalin fixed or paraffin wax embedded, provided the appropriate procedures are followed. 0.5-1 μg of DNA is sufficient for the CGH experiment, though if the desired amount is not obtained DOP-PCR may be applied to amplify the DNA, however it in this case it is important to apply DOP-PCR to both the test and reference DNA samples to improve reliability.