Analytical technologies are used at various clinical sites. In particular, recent developments of analytical chemistry potentiate the usefulness of analytical chemistry in the medical front. The department of pharmaceutical sciences in our hospital has a lot of advanced analytical technologies. Many clinical chemical studies are being developed by analytical technologies and the many analytical methods are used in routine medical care. A new chemical diagnostic method has been developed by a highly accurate and precision LC/MS/MS quantification method and metabolomics technologies. The LC/MS/MS technique is also used for the analysis of the poison substances in patients with the intoxication of some drug or poison. In addition, LC/MS/MS analyses play important roles for the highly precision therapeutic drug monitoring; they are expected to contribute to the advancement of precision- or personalized medicine.