A study was conducted to determine the potential of two-liquid phase-bioreactors for the treatment of (polycyclic aromatic hydrocarbons) PAHs. Phenanthrene and pyrene were supplied two times at a concentration of 100 mg/l of reactor broth. either as crystals or dissolved in silicone oil. Complete phenanthrene biodegradation was achieved within 3 days after each addition to the biphasic-inoculated reactor. Its concentration in the monophasic reactors dropped by 93% within 4 days, but remained incomplete for the duration of the experiment. Pyrene removal occurred to a limited extent only in the presence of phenanthrene. Significant pollutant losses were recorded in the monophasic reactors, most likely caused by volatilization. Pollutant degradation was improved upon repeated phenanthrene amendment to the biphasic system. Biphasic reactors allow the fast and complete degradation of PAHs and prevent their hazardous disappearance. The use of biphasic reactors for the degradation of poorly soluble pollutants should become more beneficial when the substrate-interface uptake mechanism is operating. Thus, biphasic reactors should be integrated into the microbial enrichment procedure.