The NOR-SWITCH Study

Inclusion Criteria: 1. A clinical diagnosis of either rheumatoid arthritis, spondyloarthritis, psoriatic arthritis, ulcerative colitis, Crohn's disease or chronic plaque psoriasis 2. Male or non-pregnant, non-nursing female 3. \>18 years of age at screening 4. Stable treatment with innovator infliximab (Remicade) during the last 6 months 5. Subject capable of understanding and signing an informed consent form 6. Provision of written informed consent Exclusion Criteria: 1. Major co-morbidities, such as severe malignancies, severe diabetic mellitus, severe infections, uncontrollable hypertension, severe cardiovascular disease (NYHA class 3 or 4) and/or severe respiratory diseases 2. Change of major co-medication during the last 2 months prior to randomization: RA, SpA and PsA: Initiation of systemic corticosteroids or synthetic DMARDs or other medication which according to the investigator would interfere with the stability of the disease. UC and CD: Initiation of systemic corticosteroids or an immunosuppressant or other medication which according to the investigator would interfere with the stability of the disease Psoriasis: Initiation of synthetic DMARDs or other medication which according to the investigator would interfere with the stability of the disease 3. Inadequate birth control, pregnancy, and/or breastfeeding 4. Psychiatric or mental disorders, alcohol abuse or other substance abuse, language barriers or other factors which makes adherence to the study protocol impossible 5. Change in treatment with innovator infliximab (Remicade) during the last 6 months due to disease related factors, not including dose/frequency adjustments due to drug concentration measurements