It has been found that nickel and vanadium are the major heavy-metal contaminants present in spent FCC catalysts. Standard leach tests produced vanadium levels in the leachate in excess of the current environmental limits. Therefore the disposal of spent FCC catalysts in landfill sites must be regarded as environmentally dangerous. Spent catalysts can be effectively stabilised by mixing them with cement. The stabilised catalyst is safe for landfill disposal.