Differential Display

[yd128 at albnyvms.bitnet]

Hello everyone:  I am working on differential display.  On the gel, I do see some specific bands.  After cut these bands, reamplified by PCR, I did Northern Blot using the PCR rpoducts as probe.  However, I have not getten any positive bands in Northern Blot.  Does anybody work use differential display?  What is the possibility of false positive?  Any suggestion.  e-mail to yd128 at albanyvms.   
Thanks.