Abstract: The present invention relates to a method for determining absorption of cobalamin or analogues thereof in an individual comprising (ii providing two blood samples from said individual, wherein the first sample comprises said individual's blood prior to ingestion by said individual of non-radioactive cobalamin or an analogue thereof and the second sample comprises said individual's blood after said ingestion, (ii) determining the concentration of cobalamin or analogue thereof in the first sample, (iii) determining the concentration of cobalamin or analogue thereof in the second sample by treating complexes of cobalamin or analogue thereof and one or more carrier proteins with one or more enzymes to release cobalamin or analogue thereof from said one or more carrier proteins, and (iv) determining, on the basis of comparison of said concentrations in said two samples, whether said cobalamin or analogue thereof has been absorbed in the blood stream.