Despite its undoubted benefit in patients with inflammatory bowel disease, anti-TNF therapy has some limitations including the lack of primary response and the loss of response to treatment in some patients. An empirical approach to these problems is frequently used based on clinical outcome. The measurement of anti-TNF drug serum levels and anti-drug antibodies (ADAb) levels has been proposed for improving the management of anti-TNF drugs. Although their role in routine clinical practice has not been clearly defined, current data support their relationship with clinical outcomes and suggest their clinical utility primarily in patients with loss of response to anti-TNF agents. The presence of pre-existing ADAb before starting the anti-TNF therapy has recently been described. Transient ADAb, non-neutralizing ADAb and some cut-offs points have been proposed, extending the knowledge about this topic. A standardized and widely available test with cut-off points for each anti-TNF agent and the definition of the most appropriate actions to be taken given the serum concentration of the drugs and ADAb are needed before recommending their routine use.