An inexpensive method was developed to measure local gas holdup based on withdrawal of the air-liquid dispersion in bioreactors under non-isokinetic conditions. The method was tested with several suction probe designs and withdrawal pressures using coalescing and non-coalescing model media as well as during yeast fermentations. Simultaneously, gas holdup was measured manometrically. With a straight end probe and vacuum pressure of 3 kPa, local gas holdup measurements presented a relative error < 6% compared to the manometric method, independently of the media composition. This method was used to characterize local gas holdup in a bubble column. Two new parameters are proposed to characterize non-gassed volume and gas holdup homogeneity. (c) 2005 Elsevier Ltd. All rights reserved.