The present invention concerns a reagent composition for releasing vitamin D compounds bound to vitamin D-binding protein, a method for the detection of a 25-hydroxyvitamin D compound in which the 25-hydroxyvitamin D compound is released from vitamin D-binding protein using this reagent and the mixture obtained in this manner is analyzed, the use of the reagent to release vitamin D compounds as well as a kit for detecting 25-hydroxyvitamin D which contains the reagent for releasing vitamin D compounds in addition to the usual immunological reagents.
