SCA Screen ELISA is a solid phase enzyme immunoassay (ELISA) employing highly purified mannan for the combined quantitative detection of anti-Saccharomyces cerevisiae IgA and IgG antibodies (ASCA) in human serum. ASCA recognize specific mannan, a component of the outer cell wall of yeast. The assay is highly specific and sensitive for Crohn`s disease. Crohn‘s disease is one of the two major Inflammatory Bowel Diseases (IBD). IBD is an umbrella term, that covers both primary disorders causing inflammation or ulceration in the small and large intestine, Crohn‘s disease and ulcerative colitis. Crohn‘s disease affects both, the small bowel and the colon, unlike ulcerative colitis which is restricted to the colon only. The etiology is not revealed yet, although a genetic and infectious background for the disease is under discussion. Colonoscopy and ileoscopy are the established tools of diagnosis, no serology was available so far. Though Crohn‘s disease and ulcerative colitis share several symptoms the course of the diseases, its complications and its management are different, especially when it comes down to surgery. Consequently the differental diagnosis of both diseases is crucial prior to treatment. Aggravating, about 5-10% of the patients can not be distinguished clearly by existing available diagnostic methodologies and are referred to as indeterminate colitis. ASCA have been found to be specific markers for Crohn`s disease. They have been reported for these patients with a frequency of 68%. The identification of the target antigen mannan, a mannose-rich carbohydrate antigen of the outer cell wall of yeast, enabled the detection of ASCA by enzyme immunoassay. Being the first available highly specific serological marker, ASCA may become an important tool for the difficult task of diagnosing IBD. Moreover its high positive predictive value offers the only possibility of a convenient and reliable screening and monitoring of risk groups.