Ammonia nitrogen is one of the most common inhibitors in the anaerobic digestion of complex wastes containing high concentrations of ammonia like animal manures, blackwater and waste oil from gastronomy. The inhibiting effect of ammonia on methanogenesis has been well established. In contrast, the knowledge on the effect of ammonia on organic matter hydrolysis is rather limited. This study focuses on evaluating the effect of ammonia on the hydrolysis of carbohydrates and lipids, which are commonly found in biomass. Batch digestion of tributyrin and cellulose at varying ammonia concentrations were performed, using biomass adapted to 4.9 g NH4+-N.l(-1). From this experimental study it was concluded that total ammonia nitrogen in the range of 2.4-7.8 g NH4+-N.l(-1) (283-957 mg NH3-N.l(-1)) does not inhibit the hydrolysis of tributyrin or cellulose. This result is further confirmed by mathematical analysis of the estimated variation of the first-order hydrolysis constant as a function of the total ammonia concentration. (C) 2012 Elsevier Ltd. All rights reserved.