A method for washing laundry during a washing cycle in a laundry washing machine comprising: - a washing drum adapted to receive laundry; - a washing tub external to said washing drum ; - a water supply unit to supply water (W) into said washing tub ; - an automatic dosing device to supply detergent (D) into said washing tub comprising a compartment suitable for receiving a quantity of detergent (D) sufficient for a plurality of washing cycles; - a first recirculation circuit suitable for withdrawing liquid from a bottom region of said washing tub and for re-admitting such a liquid into said bottom region of said washing tub ; - a concentration sensor device arranged in said first recirculation circuit or at said bottom region of said washing tub ; - a control unit for controlling functioning of said laundry washing machine ; wherein the method comprises an initial phase comprising the steps of: a) introducing a first prefixed quantity (Q1d; Q1'd) of detergent (D) into said washing tub ; b) introducing a first prefixed quantity (Q1w) of water (W) into said washing tub ; c) activating said first recirculation circuit for mixing said first prefixed quantity (Q1d; Q1'd) of detergent (D) with said first prefixed quantity (Q1w) of water (W) at said bottom region of said washing tub ; d) providing data from said concentration sensor device to said control unit relating to the concentration of said detergent (D) for determining the current concentration value (V) of said detergent (D); e) comparing said current concentration value (V) of said detergent (D) with one or more prefixed concentration levels (T1, T2; T1') stored in said control unit and either introducing a second quantity (Q2d; Q2'd) of detergent (D) or not introducing any quantity of detergent (D) into said washing tub according to the result of said comparison; wherein said first prefixed quantity (Q1d; Q1'd) of detergent (D) and/or said second quantity (Q2d; Q2'd) of detergent (D) is determined on the base of the amount of laundry load (L); wherein after said initial phase the method comprises at least a step of washing said laundry by rotating said washing drum during which the laundry is subjected to a mechanical action and at least a step of draining dirty liquid from said washing tub to the outside. - a washing drum adapted to receive laundry; - a washing tub external to said washing drum ; - a water supply unit to supply water (W) into said washing tub ; - an automatic dosing device to supply detergent (D) into said washing tub comprising a compartment suitable for receiving a quantity of detergent (D) sufficient for a plurality of washing cycles; - a first recirculation circuit suitable for withdrawing liquid from a bottom region of said washing tub and for re-admitting such a liquid into said bottom region of said washing tub ; - a concentration sensor device arranged in said first recirculation circuit or at said bottom region of said washing tub ; - a control unit for controlling functioning of said laundry washing machine ; a) introducing a first prefixed quantity (Q1d; Q1'd) of detergent (D) into said washing tub ; b) introducing a first prefixed quantity (Q1w) of water (W) into said washing tub ; c) activating said first recirculation circuit for mixing said first prefixed quantity (Q1d; Q1'd) of detergent (D) with said first prefixed quantity (Q1w) of water (W) at said bottom region of said washing tub ; d) providing data from said concentration sensor device to said control unit relating to the concentration of said detergent (D) for determining the current concentration value (V) of said detergent (D); e) comparing said current concentration value (V) of said detergent (D) with one or more prefixed concentration levels (T1, T2; T1') stored in said control unit and either introducing a second quantity (Q2d; Q2'd) of detergent (D) or not introducing any quantity of detergent (D) into said washing tub according to the result of said comparison; <EOS>