Vitamin D (D) plays important roles for homeostasis of serum calcium and so
on, in human after metabolic activation. The measurements of concentration
s of D metabolites in biological fluids are important for clinical and nutr
itional diagnoses. In these respects, developments of analysis of D metabol
ites, especially the phase I reaction products (free metabolites), have bee
n carried out. In the first part of this report, the advancein developments
of analysis of the free metabolites is reviewed according to the methodolo
gy over the last five years. The phase II reaction products (conjugated met
abolites) of D, which are poorly understood compared to the free metabolite
s, are recently found in many kinds of animals, and much interest is focuse
d on their physiological roles. In the second part, an overview of the iden
tification and quantification of the conjugated D metabolites in biological
fluids is presented mainly from our studies.