[BioC] (stupid) question about wilcoxon test and finding interesting genes

[Dipl.-Ing. Johannes Rainer]

hi,
i must excuse myself for my question, but i'm not really good in statistics...

we have done affymetrix genechips with samples from patients before and 
after treatment. until now i searched for genes that are influenced by 
the treatment using M values but i wanted also to apply a statistical 
test to get some proof that the genes i found are significant.

so i applied a wilcoxon paired test to the expression values (one test 
per gene). my samples size is 13 (13 chips with samples before 
treatment and 13 afterwards). i subtracted the values after treatment 
from those before treatment (

p.vals <- apply((untreated-treated),MARGIN=1,wilcox.test) , untreated 
is a matrix with 13 columns and 54000 rows (genes) and the same is 
treated). according to the p values i got nearly every gene is 
significant, also if the gene is not regulated.

so my question, do i have to correct the p values or was i totally 
wrong with the assumption to get significant (and regulated) genes in 
this way?

thanks