The use of biological drugs consisting of large molecules has in recent years expanded to new indications and new specialties. These drugs are most commonly proteins possessing the structure of an antibody or a receptor, and treatment with them is significantly more expensive than that carried out with conventional small molecule drugs. Determination of drug levels and emerging antibodies form the basis of individualization. They will enable better treatment results with simultaneous avoidance of unnecessary medications, excessive doses--and extra costs. We demonstrate the individualization of TNF-α blocker therapy through patient cases in various situations.