In the present study, we have investigated the biotransformation of different aromatic compounds to their cis-dihydrodiols (cis-diols) with immobilized Pseudomonas putida UV4 cells using barium alginate as the immobilization medium for the cells in a fluidized-bed reactor. The reactions have been performed in a biphasic system containing 20% (v/v) tetradecane. The bacterial beads were fluidized using a flow of pure oxygen at a flow rate of tao mi min(-1). The production of toluene cis-diol under the same conditions by the recombinant organism Escherichia coli JM109 (pKST11) was compared. The production of toluene cis-diol with E. coli JM109 (pKST11) was more than 24 times higher that the values reported in the literature using similar recombinant non-immobilized organisms. The capacity of immobilized E. coli JM109 (pKST11 to yield cis-diols from different aromatic substrates in small-scale biotransformations was also investigated.