Hi Brade,
As as long as you haven't applied the biotinylated secondary antibody 
and third step streptavidin-reagent, you don't have any problem with 
biotin blocking after the primary antibody.
The trick of usual 2-step biotin-blocking kits is to bind (strept)
avidin to the intrinsic biotin in the tissue section first and then to 
saturate the left-over binding sites at the (strept)avidin molecule 
with free d-biotin. 
Good luck
Chris van der Loos
Dept. of Cardiovascular Pathology
Academical Medical Center
Amsterdam - The Netherlands 

----- Original Message ----- 
From  "brade, brade upland, upland"  
Date  Wed, 19 Nov 2003 20:02:23 -0800 (PST) 
To  histonet@lists.utsouthwestern.edu 
Subject  [Histonet] Biotin block after primary? 

Hi,
I accidently added my primary antibody before avidin/biotin blocking.  
Is it possible to block after the primary but before a biontinylated 
secondary?  Thank you for help.



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