Switching to Adalimumab has proven to be efficacious in Crohn's disease (CD) patients with intolerance or loss of response to Infliximab. Currently there are no studies on the efficacy of switching to Infliximab in patients with loss of response or primary non-response to Adalimumab. Even in rheumatology, where switching between all classes of anti-TNFα biologicals is common practice, there are no scientific data on switching from humanized to chimeric anti-TNFα antibodies.||The purpose of this study is to document the efficacy of such a switch and to identify the possible predictive factors for success.||If treatment with Adalimumab fails (despite optimal dose and interval) and the treating physician therefore decided to switch to infliximab, the patient may be enrolled in this observational study. At regular intervals (every Remicade), the patient will be clinically re-evaluated. The disease activity score will be calculated: Crohn's disease activity index (CDAI). At regular intervals, the results of interim blood tests will be documented (3x). The succession will be 1 year. At week 10, 26 and 52, additional serum samples will be taken for determination of antibodies against Adalimumab and Infliximab. The serum levels of Adalimumab (week 0) and Infliximab (week 10, 26 and 52) will be determined.||For this study there is no specific therapy change. The study wants only to document the results of a therapy switch that, in current clinical practice, is made by the treating physician.