A microbial amperometric sensor based on the yeast Arxula adeninivorans LS3 was tested for its suitability to measure the biochemical oxygen demand incurred by the use of high molecular weight substances, such as starch, cellulose and milk powder. As with other sensors, the untreated samples varied strongly from the corresponding BOD5. Digestion of macromolecules with alpha -amylase, cellulase and protease for 30 min at 37 degreesC resulted in sensor BOD values which correlated better with BOD, values when corrected for the enzyme blank signal.