In this cross sectional and longitudinal study, patients with inflammatory bowel disease on biological treatment with infliximab or adalimumab will be included.||After inclusion, the dosage of their existing biological therapy will be adjusted following regular trough-level and antibody-level monitoring, according to a treatment algorithm.||Disease activity markers, fatigue and QoL will be assessed during the study. The hypothesis is that therapeutic drug monitoring may improve clinical disease outcome after one year of follow-up.