Cell hydrophobicity effects on the activity/stability of microorganisms of a mixed culture, selected on 2,4,6-trichlorophenol (2,4,6-TCP) in both biphasic aqueous-silicone oil and monophasic aqueous continuous systems was determined. The mixed culture composed of Pseudomonas, strains SP1 and SP2, Arthrobacter sp. AR2 and Alcaligenes sp. AL2 was cultured at dilution rates from 0.033 to 0.22 h(-1). High dilution rates permitted the selection of Pseudomonas cells in both systems, with a higher cell concentration in biphasic system. Selected cells proportion with a high cell adhesion capacity increased as a function of the cell hydrophobicity, which was high at high dilution rates. The degradation rate which also increased as a function of the dilution rate in both systems, was about two times higher in the biphasic system than in monophasic one. The results indicate that the cell hydrophobicity, which increases with the growth rate, is a key factor in the selection and activity of xenobiotic-degrading microorganisms. Therefore, microbial selection and xenobiotics biodegradation at high dilution rates could be favored in reactors containing solid or liquid surfaces.