Abstract: A method of stabilizing a fluidized bed in a fluidized bed roasting process for metal sulphide concentrate comprises the step of controlling the particle size distribution of the particulate material in the bed so that a minimum amount of no less than about 30% of the concentrate falls in a size range of from about 100 to about 420 microns. The minimum amount preferably falls in the range of from about 35% to about 40%. In one embodiment of the invention the particle size distribution is controlled by maintaining the amount of lead in the concentrate in a range from about 3% to about 4%, preferably 3.7% to about 3.8%. In another embodiment the particle size distribution is controlled by using a pelletized feed or by the combination of the steps of using a pelletized feed and regulating the lead content of the concentrate.