If you are working in an EM lab, access to osmium tetroxide is fairly
straight forward.  If you
are in a routine histopathology laboratory without a fume hood, handling
this chemical requires
care, or you fix your corneas from the fumes, etc.  Not a good thing.  For
those interested in
enhanced DAB reactions, it is easier to access one already available in a
kit.  There are some
excellent products on the market from any immunochemical supplier.  We have
gone to a Pierce
enhanced DAB kit, a two step process with the enhancer as part of the
chromagen reagent, just
mix with  buffer.  Kits available  from Vector, Zymed, Biogenex, etc,
etc.  One still has to collect DAB for hazard reasons but having to throw
in making up
osmium never appealed to us, there are other enhancing reagents used,  that
work
well and probably a tidge safer to handl if you want to make inhouse
reagents.

Gayle Callis