Crossflow microfiltration of yeast solutions was performed with crossflushing (done by stopping the permeate flow while maintaining the flow across the membrane) at intervals of 0.5 to 6 min and lasting for 5 to 90 s. A quantitative method was determined to compare the effectiveness of the various crossflushing times, independent of the initial cleanliness of the membrane. If crossflushing is performed every 0.5 to 1 min, 10-15 s is required to affect the steady-state flux. More time is required if crossflushing is performed less frequently. The total crossflushing time is also important. The more time spent crossflushing, the more slowly flux declines. However, since no product is being purified during crossflushing, economics will be an important part of determining the optimal crossflushing time.