Abstract High Intensity Conditioning improved pentlandite flotation from a nickel ore. Specifically, High Intensity Conditioning increased the flotation rate of pentlandite contained in the 8 to 75 μm particle size range. There was also a significant increase in the maximum recovery of pentlandite over the same particle size range. By contrast, the rate and maximum recovery of pentlandite contained in particles less than 8 μm were not significantly increased by High Intensity Conditioning. Desliming was affected by hydrocycloning to remove particles less than 8 μm in size from the ground ore. Desliming caused similar changes in the size-by-size flotation behaviour of pentlandite as High Intensity Conditioning. Mechanisms of High Intensity Conditioning are discussed in terms of the particle size dependent flotation behaviour of pentlandite.