Dehydrogenase enzymatic activity was determined to monitor the biological activity in a composting process of organic fraction of municipal solid waste. Dehydrogenase activity is proposed as a method to describe the biological activity of the thermophilic and mesophilic stages of composting. The maximum dehydrogenase activity was detected at the end of the thermophilic stage of composting, with values within 0.5-0.7 mg g dry matter(-1) h(-1). Also, dehydrogenase activity can be correlated to static respiration index during the maturation mesophilic stage. (C) 2007 Elsevier Ltd. All rights reserved.