Terry,

The following treatment is used after a PBS rinse and is followed by PBS
rinses prior to the application of a blocking serum or primary Ab step.

immerse slides in fresh 0.3% H2O2 prepared in 0.1% Sodium Azide(aq)  for
10-15 minutes

prepare fresh and place in coplin jar
3% H2O2 	5ml
0.1% NaAzide	45 ml

Dispose of Na azide solution in accordance with local and other regulations.

Reference:
Title 
     Use of azide and hydrogen peroxide as an inhibitor for endogenous
peroxidase
     in the immunoperoxidase method.
Source 
     J HISTOCHEM CYTOCHEM 35:1457-1460,
     DECEMBER, 1987.

This works very well,
Tim



> -----Original Message-----
> From:	t.hacker@har.mrc.ac.uk [SMTP:T.Hacker@har.mrc.ac.uk]
> Sent:	Thursday, May 31, 2001 10:31 AM
> To:	'Histonet'
> Subject:	endogenous peroxidase
> 
> What are you using for blocking endogenous peroxidase in acetone 
> fixed frozen sections?
> I have used a weak solution of H202 which is not always effective, 
> too strong and I get excessive "bubbling" of the tissue. Yes, I 
> know, try a strength in between, but I was wondering if there is 
> something more appropriate and less aggressive.
> I look forward to a wealth of knowledge and experience, preferably 
> by 9am GMT tomorrow.
> Many thanks,
> Terry.
> Terry Hacker,r
> Medical Research Council,
> Harwell,
> Didcot,
> Oxfordshire, OX11 ORD
> 01235 834393 x360