Tumor necrosis factor alpha (TNFα) is a cytokine with a critical role in the pathogenesis of some chronic inflammatory diseases, such as inflammatory bowel diseases. Anti-TNF agents, which neutralize the biological activity of TNFα, are widely used among the different therapeutic options for the treatment of patients with inflammatory bowel diseases. These drugs are very useful in clinical practice, but some patients experience lack and loss of response during the treatment. Drug serum concentration, antibodies against anti-TNF agents, clearance of the drug, formation of immune complexes, a more severe disease and probably other unknown factors can influence the treatment's efficacy. Nowadays, the management of patients with lack or loss of response is empirical. The measurement of drug concentrations and antibodies against anti-TNF agents might be useful for improving the selection of patients that will benefit from the maintenance treatment. In clinical practice, these methods may help us decide which strategy will be used in cases of loss of response: treatment intensification, shortening the infusion interval, increasing the dose, switching to another anti-TNF agent or to a drug with another mechanism of action. The optimal strategy in the future may be comprised of an early detection of loss of response to the treatment by assessing clinical symptoms and finding evidence of activity of the disease on endoscopic or radiological examinations when necessary, as well as a better management of anti-TNF treatment aided by measuring the serum concentration of the drug and antibodies against the drug.