confusing PCR - (Jan/19/2011 )

Hi everybody.
Bands in my PCR sometimes appear and sometimes disapper. I did PCR yestersay for 5 sicks, but only one of them had band although all circumstance were same. I confusd really.

When a PCR assay works sometimes and does not work others it is typically due to the fact that the assay is not robust (assuming you are using the same DNAs so it is not a DNA issue). Your best bet is to either optimize the PCR assay, if you have not done it already, or to design a new assay.