Oligonucleotide probing

[LAFLAMME at MAINE.BITNET]

Does anyone out there in netland have any experience in the use of
oligonucleotide probes to screen total DNA in northern or slot-blots?
I have been using 20 mers to pick out individual members of a family
of plant genes.  It seems that the method is not sensitive enough to
detect these sequences in a sample containing a HUGE excess of
non-hybridizing species.  If anyone could pass along a helpful hint
I would be very happy.  I would prefer not to isolate poly A RNA due
to the extra hassle and the possibility of skewing the final results.