A flotation method for recovering valuable metal containing ore particles from ore particles suspended in slurry, wherein - the ore particles are ground in a grinding step, - the ore particles are classified in a classifier from which at least the overflow is conducted as a slurry feed to a treatment system comprising at least two flotation cells (41, 42) of which at least one is an overflow flotation cell operated with constant slurry overflow - the slurry is treated in the at least one overflow flotation cell by introducing flotation gas bubbles into the slurry and by creating a continuous upwards flow of slurry in the vertical direction of the first flotation cell, - at least part of the valuable metal containing ore particles are adhered to the gas bubbles and rise upwards by buoyancy, at least part of the valuable metal containing ore particles are adhered to the gas bubbles and rise upwards with the continuous upwards flow of slurry, and at least part of the valuable metal containing ore particles rise upwards with the continuous upwards flow of slurry, - the valuable metal containing ore particles are recovered by conducting the continuous upwards flow of slurry out of the at least one overflow flotation cell as slurry overflow, - the volumetric flow rate of the slurry overflow is analysed and the flow rate of the slurry feed is controlled accordingly so that a continuous slurry overflow is generated, and - at least part of the slurry overflow is conducted to a further treatment step (420, 430, 44) in the treatment system, the system characterized in that the at least one overflow flotation cell is operated with virtually no froth depth or froth layer. - the ore particles are ground in a grinding step, - the ore particles are classified in a classifier from which at least the overflow is conducted as a slurry feed to a treatment system comprising at least two flotation cells (41, 42) of which at least one is an overflow flotation cell operated with constant slurry overflow - the slurry is treated in the at least one overflow flotation cell by introducing flotation gas bubbles into the slurry and by creating a continuous upwards flow of slurry in the vertical direction of the first flotation cell, - at least part of the valuable metal containing ore particles are adhered to the gas bubbles and rise upwards by buoyancy, at least part of the valuable metal containing ore particles are adhered to the gas bubbles and rise upwards with the continuous upwards flow of slurry, and at least part of the valuable metal containing ore particles rise upwards with the continuous upwards flow of slurry, - the valuable metal containing ore particles are recovered by conducting the continuous upwards flow of slurry out of the at least one overflow flotation cell as slurry overflow, - the volumetric flow rate of the slurry overflow is analysed and the flow rate of the slurry feed is controlled accordingly so that a continuous slurry overflow is generated, and - at least part of the slurry overflow is conducted to a further treatment step (420, 430, 44) in the treatment system, the system characterized in that the at least one overflow flotation cell is operated with virtually no froth depth or froth layer.