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 into said washing tub; - an automatic dosing device to supply detergent into said washing tub comprising a compartment suitable for receiving a quantity of detergent 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 into said washing tub; b) introducing a first prefixed quantity (Q1w) of water into said washing tub; c) activating said first recirculation circuit for mixing said first prefixed quantity (Q1d; Q1'd) of detergent with said first prefixed quantity (Q1w) of water 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 for determining the current concentration value of said detergent; e) comparing said current concentration value of said detergent 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 or not introducing any quantity of detergent into said washing tub according to the result of said comparison; wherein said first prefixed quantity (Q1d; Q1'd) of detergent and/or said second quantity (Q2d; Q2'd) of detergent is determined on the base of the amount of laundry load. - a washing drum adapted to receive laundry; - a washing tub external to said washing drum; - a water supply unit to supply water into said washing tub; - an automatic dosing device to supply detergent into said washing tub comprising a compartment suitable for receiving a quantity of detergent 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 into said washing tub; b) introducing a first prefixed quantity (Q1w) of water into said washing tub; c) activating said first recirculation circuit for mixing said first prefixed quantity (Q1d; Q1'd) of detergent with said first prefixed quantity (Q1w) of water 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 for determining the current concentration value of said detergent; e) comparing said current concentration value of said detergent 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 or not introducing any quantity of detergent into said washing tub according to the result of said comparison;