Method in an exhaust treatment system for treatment of an exhaust stream, which results from a combustion in a combustion engine, and comprises nitrogen oxides NO x, including: - a first supply of a first additive into said exhaust stream, through the use of a first dosage device, arranged in said exhaust treatment system; characterised by: - a first reduction of a first amount of nitrogen oxides NO x_1 reaching a first device, arranged downstream of said first dosage device, in order to reduce said first amount of nitrogen oxides NO x_1 through the use of said first additive, wherein said first reduction comprises a first reduction of said first amount of nitrogen oxides NO x_1, through a first selective catalytic reduction catalyst (SCR 1), followed by a reduction of nitrogen oxides NO x, and oxidation of potential additive in said exhaust stream, through a first slip-catalyst (SC 1); - a second supply of a second additive into said exhaust stream, through the use of a second dosage device, arranged downstream of said first device; and - a second reduction of a second amount of nitrogen oxides NO x_2 reaching a second device, arranged downstream of said second dosage device, in order to reduce said second amount of nitrogen oxides NO x_2 through the use of said first and/or second additive; wherein - at least one of said first supply and said second supply is controlled, based on an overall ability for said first device to provide said first reduction, and for said second device to provide said second reduction, so that a required total reduction of said nitrogen oxides NO x in said exhaust stream is provided by said exhaust treatment system; and - said control of said first supply of said first additive results in an increase of said first supply of said first additive, which is carried out in such a way that a slip of additive out from said first selective catalytic reduction catalyst (SCR 1) arises and is substantially stored, and/or oxidised, in said first slip-catalyst (SC 1). - a first supply of a first additive into said exhaust stream, through the use of a first dosage device, arranged in said exhaust treatment system; - a first reduction of a first amount of nitrogen oxides NO x_1 reaching a first device, arranged downstream of said first dosage device, in order to reduce said first amount of nitrogen oxides NO x_1 through the use of said first additive, wherein said first reduction comprises a first reduction of said first amount of nitrogen oxides NO x_1, through a first selective catalytic reduction catalyst (SCR 1), followed by a reduction of nitrogen oxides NO x, and oxidation of potential additive in said exhaust stream, through a first slip-catalyst (SC 1); - a second supply of a second additive into said exhaust stream, through the use of a second dosage device, arranged downstream of said first device; and - a second reduction of a second amount of nitrogen oxides NO x_2 reaching a second device, arranged downstream of said second dosage device, in order to reduce said second amount of nitrogen oxides NO x_2 through the use of said first and/or second additive; wherein - at least one of said first supply and said second supply is controlled, based on an overall ability for said first device to provide said first reduction, and for said second device to provide said second reduction, so that a required total reduction of said nitrogen oxides NO x in said exhaust stream is provided by said exhaust treatment system; and - said control of said first supply of said first additive results in an increase of said first supply of said first additive, which is carried out in such a way that a slip of additive out from said first selective catalytic reduction catalyst (SCR 1) arises and is substantially stored, and/or oxidised, in said first slip-catalyst (SC 1).