Operating conditions of crossflow microfiltration (MF) of sweet cheese whey were found to influence the process performance. The evolution of fouling during different sets of operating parameters (permeation flux, flow velocity) modelled according to a modified "complete pore blocking" model supports a mechanism of deposit build-up ruled by a competition between convection and erosion. Fast or slow transient conditions to reach the desired constant permeation flux level resulted in different fouling behaviour. Proteins were better transmitted when permeation flux was increased instantaneously while resulting in lower filtered volume compared to a gradual permeation flux increase. A different combination of steady permeation flux and tangential flow velocity also affected MF performance. It was shown that the lower the ratio permeation flux, J/wall shear stress, tau(w), the better the performance (increased operating time and amount of proteins recovered at the end of MF). It looks as if a range of large ratio J/tau(w) exists, where fouling increased faster and MF operating time was dramatically shortened.