 Patients with autoimmune diseases like inflammatory bowel disease IBD and rheumatoid arthritis RA are at increased risk of infections. This increased susceptibility to infections is due to the disease itself, but also be-cause many patients with autoimmune conditions are treated with immuno-suppressive drugs. Different drugs are well-known suppressors of the immune system: Prednisolone, Azathioprine, Methotrexate MTX, TNF-a inhibitors, and the newer biological agents such as, e.g., Rituximab RTX, which is a drug used in the treatment of RA patients often in combination with MTX. The extent of immunosuppression induced by these therapeutic agents seems to depend, to some extent, on pharmacological doseresponse relationships and on the combination of drugs, but individual variability plays a major role as well. 