Dana,
I agree with you that fesh tissue is generally higher in background. Some of
this is really not "background" but detection of low levels of material which
may not be evident when the tissue is fixed. On the other hand, some
background may  be from diffusion of materials.
The main point is that fresh tissue has less overall artifacts than fixed
tissue but tissue integrity and diffusion of materials may be an important
factor.
Barry


DDittus787@aol.com wrote:

> Fresh frozen tissue is notorious for high background , it is my experience
> that if you shorten incubation time , you will get less background., and
> fresh tissue seems to need less time on all reagents, simply because it is
> fresh.
>                                                          Dana