HI, it would be nice to tell us which kits you tried. Cheers, Nadine

Do not expect to obtain much DNA from archived samples, especially if they have been archived for 15 years. Since formalin fixed samples undergo extensive crosslinking it is difficult to extract nucleic acids from them. If the samples have been in formalin for 15 years it is unlikely that any DNA can be obtained. You may have better luck with samples that have been fixed in formalin and then embedded in paraffin.

I am not aware what kits you are using. Make sure that the kit has a protease digestion step (usually Proteinase K). First try the digestion overnight; if that does not work try digesting for up to 36-48 hours. This step will break down the crosslinked proteins and (hopefully) release any DNA that remains.

Here is a protocol: http://scholarsresearchlibrary.com/ABR-vol3-iss7/ABR-2012-3-7-3174-3177.pdf . However, do not expect high yields. In this protocol they used 100 mg of muscle tissue and their oldest sample (25 years) only produced about 9 µg of low quality DNA.

If you haven' tried it yet, Qiagen kits normally produce good results with anything DNA-extraction: http://www.qiagen.com/products/catalog/sample-technologies/dna-sample-technologies/genomic-dna/qiaamp-dna-ffpe-tissue-kit

Thanks for the replies.

@Nadine, we tried Qiagen kit for FFPE tissue and Norgen's kit.

@ Sabyasachi, we tried PK digestion for different time peroids like 1 to 3 days. And we did run 5ul of DNA on agarose gel and could see smear below 200 base pairs and our ACTB primer should amplify @~150bps.

@ Patrick, we did try the Qiagen and not much luck. And thanks for the link will try this soon, eventhough our protocol is similar to that but without DTT and less of SDS.

And one more thing we've noticed is that after the 70% ethanol wash a white precipitate is there. Is it because of too much SDS or ?