It is the need of the hour to speed up the development of new compounds in the pharmaceutical industry. At the early stages of drug development, many compounds are screened as rapidly as possible to identify the optimal lead compounds. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is essential for high-throughput quantitative analysis of the compounds. Because LC-MS/MS is more sensitive and selective for biological samples than other methods, it is popular in various fields, including pharmacokinetics and toxicokinetics. High-throughput analysis with LC-MS/MS plays a key role in speeding up drug discovery.In recent years, many developments in high-throughput analytical methods based on quantification by LC-MS/MS are reported to simplify sample preparation and speed up the analysis of the compounds.1-5) Among them, turbulent-flow chromatography, which uses turbulence caused by a high flow rate, is one method to separate the analyte from the biological matrices by the size-exclusion mechanism and hydrophobic interactions. 6,7) This method is advantageous in that it is applicable in a wide range of analyses by employing an online purification devise with column-switching systems. However, the technique requires specialized equipment and disposable cartridges, leading to high cost per sample. Monolithic chromatography is another example of the abovementioned developments. [8][9][10][11] This method employs the use of a monolithic column that consists of a unique stationary phase with high porosity due to the presence of double structures comprising mesopores and macropores, which enable the pressure in the column to be much lower than that in a conventional column of silica gel. Therefore, LC-MS/MS analysis can be carried out at a high flow rate using a monolithic column, speeding up the analysis. However, analysis of polar compounds such as metabolites and endogenous substances cannot be carried out using a monolithic column because the retention capability for these compounds is poorer than that of an octa decyl silyl (ODS) column and the lineup such as the bore diameter and length of monolithic column is not enough. Next, parallel LC-MS/MS method is also an option that could increase the throughput. [12][13][14] This method employs multiple HPLC systems and columns connected in parallel to an MS system, [15][16][17][18] and the eluted analyte from each HPLC system is alternately introduced into the MS system through a switching valve. Hence, the time spent before and after the elution of analytes can be diverted to detect the analytes eluted from other systems, thus considerably speeding up the analysis. However, this method requires specialized equipment and involves preparation of individual calibration curves for each system, even for the same analyte.In this study, we focused on maximizing the throughput of pharmacokinetic studies, and we developed a new method with conventional instruments, which lowers costs and effort. We named this approach multiple injection method (MIM), as multiple compound...