The biodegradation of 2-iodobenzoic acid (2IBA), 3-iodobenzoic acid (3IBA) and 4-iodobenzoic acid (4IBA) was investigated. Substrate disappearance was monitored in conjunction with product formation (ie iodide production) in order to verify complete mineralisation. Samples from SmithKline Beecham (SE) Wastewater Treatment Plants (WWTP) were employed to test their ability to degrade the iodinated aromatics listed above. Complete mineralisation of 3IBA was observed and the initial pathway(s) of biotransformation (via hydroxybenzoic acid formation) was proposed based on the comparison with standards of metabolites previously elucidated for similar halogenated benzoic acids. Evidence for co-metabolism of 4IBA was observed since biodegradation only occurred in the presence of 3IBA. No evidence of biodegradation of 2IBA was observed over a period of 20 days, neither when fed individually nor as a mixture of substrates.