The goals of this work were to test the feasibility of a continuous plug-flow (PF) bioreactor and to compare the growth in the PF bioreactor to that in a batch bioreactor. A culture of Pseudomonas putida was pumped through a tube made of Teflon with varying residence times. The culture was aerated by pumping of air simultaneously with liquid medium to provide air bubbles along the tubular culture. When the residence time in the PF bioreactor was greater than the time needed to reach the stationary phase in batch mode, the maximum biomass density reached in PF mode was the same as the maximum density reached in the batch bioreactor, and benzoate (the only carbon and energy source) was completely consumed. The drawbacks for practical application of PF were found to be fluctuations of cell concentration in the outflow cultural liquid due to cell aggregation, significant cell adhesion to the inner wall of Teflon tubing, and inadequate aeration. (c) 2005 Wiley Periodicals, Inc.