BACKGROUND Infliximab trough levels (IFX-TLs) and antibodies to infliximab (ATIs) have been suggested as useful markers for the optimization of treatment in inflammatory bowel disease (IBD). We aimed to estimate the patterns over time of IFX-TLs and ATIs in IBD patients on maintenance treatment with IFX. METHODS Two different measurements of IFX-TLs and ATIs were performed (ELISA; Eagle BioSciences) at a 10-month interval using serum samples of consecutive patients on maintenance treatment with IFX. Certain biomarkers [hemoglobin, erythrocyte sedimentation rate, C-reactive protein (CRP), platelets, albumin] measured at the same time as well as clinical disease activity and quality of life were assessed. RESULTS Among a total of 86 IBD patients under maintenance treatment with IFX, 64 [49 Crohn's disease, 15 ulcerative colitis (UC), 42 men, mean age 44.2±15.2 years, 41 in combination therapy with immunomodulator, six in intensified dose], with two available measurements of IFX-TLs and ATIs (A and B), were included in the study. The median levels of IF-TLs were 5.07 (interquartiles range: 1.60-12.73) μg/ml in measurement A and 4.68 (1.19-7.83) μg/ml in measurement B (P