A two-phase aqueous-organic system was used to degrade benzene, toluene and phenol, individually and as mixture by Pseudomonas putida F1 (ATCC 700007). In the first stage of the work, the effect of the phase ratio (0-1, v/v) and the agitation rate (150 and 200 rpm) on the biodegradation process was investigated in an orbital shaker using 2-undecanone as the solvent and the most suitable phase ratio and agitation rate were found to be 0.0625 (v/v) and 200 rpm, respectively. P. putida F1 was added into the aqueous phase of the two-phase system, which consisted of a 40 ml aqueous phase and 2.5 ml 2-undecanone. Experiments were carried out at pH 7 and 30 degreesC. Benzene, toluene and phenol individually were consumed completely below concentrations of 4400 mg l(-1) benzene, 4200 mg l(-1) toluene and 600 mg l(-1) phenol according to the aqueous phase volume. The presence of the second phase (organic phase) not only prevented the inhibition effect of the substrates, but also decreased the biodegradation time. The maximum overall biodegradation rates of benzene, toluene and phenol were obtained as 183, 197 and 18 mg l(-1) h(-1), respectively. In the biodegradation experiments using mixtures, the presence of phenol did not change the biodegradation times of benzene and toluene and, the presence of benzene and toluene decreased the biodegradation times of phenol. (C) 2004 Elsevier B.V. All rights reserved.