Infliximab and other TNF-inhibitors have revolutionised the treatment of several immunological inflammatory diseases. Still, more than half of the patients either do not respond sufficiently to infliximab therapy or loose efficacy over time. The large individual variation in the serum drug concentrations on standard doses and the development of anti-drug antibodies are thought to be main reasons for these treatment failures. An individualised treatment strategy based on systematic assessments of serum drug concentrations, therapeutic drug monitoring, has been proposed as a clinical tool to optimise efficacy of infliximab treatment. Therapeutic drug monitoring seems reasonable both from a clinical and an economical point of view, but the effectiveness of this treatment strategy still remain to be shown. The NOR-DRUM study is planned as a national, randomised controlled multicentre trial in two parts aiming to assess the effectiveness of therapeutic drug monitoring in order to achieve remission in patients with immunological inflammatory diseases starting infliximab treatment (part A) and in order to maintain disease control in patients on maintenance infliximab treatment (part B). The results of the NOR-DRUM study will hopefully contribute to an implementation of a personalised medicine approach to treatment with infliximab and other biological drugs.