Discounting regulations, generally osmium fixation can be done 
overnight at 4 deg C (refrigerator temperature). Mind, OsO4 is slow 
penetrating, and overnight might be required simply because of the 
size of the tissue blocks.
Room temp ... mayyyyyybbbeee given the tissue requirements.  But OsO4 
makes tissues brittle and crunchy, so that usually isn't a good idea.

Phil

>I'm asking this on behalf of my histologist who has been asked by a
>pathologist to modify a protocol that she has from the AFIP manual.
>When doing an osmium fixation on formalin fixed tissue, is the 8 hour
>fixing time a minimum or can it sit overnight before continuing?
>
>Thank you for any help.
>Barb Nuernberger
>Chief Toxicologist
>
>
>Medical Examiner's Office
>2100 Jefferson St.
>Jacksonville,FL 32206
>(904)630-5470
>BNuern@coj.net
-- 
Philip Oshel
Microscopy Facility Supervisor
Biology Department
024C Brooks Hall
Central Michigan University
Mt. Pleasant, MI 48859
(989) 774-3576

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