A thermostable alpha-amylase catalyzed the exothermal hydrolysis of cyclodextrins. It was immobilized covalently via a spacer on controlled pore glass (CPG-10) or Silicagel. The temperature signal caused by the reaction heat of the cyclodextrin hydrolysis was determined in a one-column calorimetric system (enzyme thermistor). It was correlated to the cyclodextrin concentration and depended on the type of enzyme carrier and kind of cyclodextrin hydrolyzed. The proposed technique offers a direct route to the determination of alpha-amylase activity, and the results are of importance for analysis of cyclodextrin concentration.