The applicability of a recently published modification of the chemostat, named "titrostat", for microbial continuous-flow purification of toluene-contaminated air is discussed. This article describes the operative range and the toluene elimination efficiency of a 2-l titrostat running with a mixed bacterial culture dominated by two Acinetobacter species: A. calcoaceticus and A. radioresistens. The study focuses on the kinetics and stoichiometry of the process. Special attention is paid to the peculiarities of toluene as an unconventional growth substrate having high carbon and energy content. Removal productivity as high as 2.24 g l(-1) h(-1) with 99.9% elimination efficiency was observed at air flow rate 60 l h(-1), temperature 32 degrees C, pH 6.2, toluene concentration in the inlet air 37.4 mg l(-1) and titrant solution containing NH3 at 1.87 g l(-1). The maximum biomass yield from assimilated toluene, Ysm=0.880+/-0.011, and a rate of substrate expenditures for cell maintenance, ms=0.022+/-0.002 h(-1), were estimated.