ABSTRACT. .The Self-Cycling Fermentation (SCF) techniql 1 e was applied to the biodegradation of several aromatic compounds by Pseudomonas putida and p"'j'eudolllomis fluorescell ..... The SCF technique was shown to be a useful research tool in aromatic biodegradation studies as weil as a potential pollution treatment method. Advantages of SCFs include stable and highly repeatable performance and almost complete substrate consumption. Biomass concentration.cycle time and the minimum dissolved oxygen level were monitored from cycle to cycle and the variation of these parameters during steady-state operation was less than 5(X,. The aromatic compounds used in this ~tudy were sodium benzoate, p-anisaldehyde and 4-methoxybenzylidine-4-n-butylaniline (MBBA). Consumptions of 93-100% were achieved for thesc compounds usingtheSCFtechnique. Consumption rates ofaromatic compounds wereshown to he considerably higher than in conventionaJ fermenters. Cycle time was found to he a usefuJ parameter forcomparing growth of ditrerent organisms on aromatic substrates. The cycle tirr.e was dependant on substrate concentration for p-anisaJdehyde. This dependence was shown to be due to the presence of an unidentified, inhibitory intermediate. .,