The aim of this work was to investigate the single exposure effect of amoxicillin on the feces composting process and the possibility of its bacterial reactivation by intermittent feeding of feces. The respiratory activity of the bacteria during the process after receiving exposure to several dosages of amoxicillin indicated a decrement of treatment performance, which was caused by the reduction of the initial viable bacterial count and activity brought about by the amoxicillin dosage. The amount of remaining feces was proportional to the initial concentration of amoxicillin, and even though no amoxicillin was detected, no automatic reactivation was observed, either. An intermittent feces feeding test was conducted to reactivate the bacteria. For the 10 and 100 mu g-amoxicillin/g dry systems, reactivation was observed, but for the 1000 mu g/g dry, no reactivation was seen. Finally, an intermittent feces feeding test was conducted with sterilized sawdust and the result indicated that the feces acted as a substrate rather than as a bacterial carrier. (C) 2006 Elsevier Ltd. All rights reserved.