The bioconversion of glycerol to dihydroxyacetone (DHA) by Gluconobacter oxydans cells was monitored by flow microcalorimetry. DHA was produced in an air-lift reactor using bacterial cells immobilized in calcium pectate gel. Glycerokinase and galactose oxidase were immobilized on controlled pore glass and used for the determination of glycerol (substrate) and dihydroxyacetone (product), respectively. Concentration values obtained by flow microcalorimetry were in a good correlation with a spectrophotometric reference method. Furthermore, flow microcalorimetry can be used for on-line monitoring of the process.