Vitamin B12 is an essential nutrient for normal DNA-synthesis and must be supplied by animal products. Vitamin B12 deficiency may cause anemia and irreverible neurological damage. Laboratory tests are used for diagnosis of vitamin B12 deficiency, and following the diagnosis, the cause of the vitamin B12 deficiency has to be clarified. For years a test called Shilling’s test has been used for evaluation of the vitamin B12 absorption. However, the Schilling’s test is no longer easy accessible because of increasing difficulties to obtain the radioactively labeled vitamin B12 requested, and native human intrinsic factor for Schilling’s test II (absorption of vitamin B12 attached to intrinsic factor) is no longer available in most countries. Recently, human intrinsic factor unsaturated with vitamin B12 has been expressed in the plant Arabidopsis thaliana. The purpose of this study was to examine whether recombinant human intrinsic factor is able to promote the uptake of vitamin B12 in patients with evident vitamin B12 deficiency.