Its proprietary. However, according to its MSDS and the
label on the bottle it contains Ammonium thiocyanate and a
wetting agent sold under the brand name Triton-X 100.
Ammonium thiocyanate was one of the substances used as a
stabilizer in the old activation/stabilization process. The
wetting agent is there probably because Sistan was intended
to be a final treatment for film and paper. However, you
have to squeegee it after treatment to avoid absorption of
an excessive amount with possible consequent staining.
  Fuji Ag-Guard performs a similar function but uses a
different chemical. AFAIK, Ag-Guard is not available in the
US.