Treatment selection for inflammatory bowel disease involves many considerations. Anti-TNF - α agents are one of the major available therapeutic tools for these diseases. Loss of response to anti- TNF - α agents is relatively common and results mostly, but not exclusively, from the development of immunogenicity against the drug. Assessment of disease activity in parallel to measurement of drug levels and anti-drug antibodies allows for treatment optimization in patients who develop clinical loss of response. For patients in remission, treatment optimization can be performed by the evaluation of risk factors for disease flare assisted by assessment of drug levels and the presence of antibodies. Various algorithms can be used to make a decision that will lead to better clinical outcomes and a better cost-effectiveness ratio. Professor Yehuda Chowers has received consultancy fees from Abbot and Schering-Plough.