The different forms of the matrix Gla protein (MGP). legend: MGP needs two posttranslational modifications for maturation: glutamate carboxylation and serine phosphorylation. Both modifications are only partially accomplished. Besides the non-modified form (dp-ucMGP) also partially modified species (dp-cMGP and p-ucMGP) and the fully maturated form p-cMGP are present in the circulation. In this paper we have tested dp-ucMGP and total ucMGP (t-ucMGP) (which consists of the sum of dp-ucMGP and p-ucMGP). Since the plasma concentration of p-ucMGP is about 10 thousand fold higher than that of dp-ucMGP, the t-ucMGP assay virtually measures p-ucMGP.