The invention relates to a method and to an arrangement for removing gaseous elementary mercury from a stream of gas and to an arrangement for carrying out the method. The arrangement comprises a first washing tower (2) for receiving a stream of gas, a second washing tower (6) for receiving a stream of once processed gas (5) from the first washing tower (2), and a third washing tower (9) for receiving a stream of twice processed gas (23) from the second washing tower (6) and configured for discharging a stream of cleaned gas (12).