A highly sensitive glucose sensor, operating in flow-injection analysis (FIA) mode, was developed for the detection of glucose in fermentation broth. The assay system is based upon the post-column reaction of the peroxide formed in the glucose-oxidase-catalysed reaction and subsequent spectrophotometric detection of the coloured product formed. The sensor system was characterised and calibrated using standard solutions, and later used for quantification of glucose in fermentation media. Two types of enzyme column were used: one operated in packed-bed mode and the other in expanded-bed mode. Both columns were integrated into a FIA system and were found to give good analytical results. Glucose concentrations as low as 0.1 mg/l and 5 mg/l could be detected in packed- and expanded-bed modes respectively. Glucose concentrations were measured during typical fed-batch fermentation conditions in this system, and the results are presented.