In dextran sulfate sodium (DSS)-induced inflammatory bowel disease in mice the relationship between the amount of ingested DSS and the severity of colitis has not been systematically investigated. We examined whether (1) the severity of colitis is DSS load-dependent, and (2) there is a critical DSS load required to reliably induce colitis. DSS load was calculated as: (drinking volume (ml) x [DSS (g)/100 ml])/body weight (g). A minimum DSS load > or = 30 mg/g body weight over 7 days resulted in a significantly elevated colonic myeloperoxidase (MPO) activity, compared to mice receiving less DSS and controls (P < 0.05). Histomorphologic data correlated with MPO activity and revealed significantly higher damage scores once the DSS load was > or = 30 mg/g body weight. Our findings demonstrate the importance of monitoring DSS load in this model of experimental colitis.