HPLC with electrochemical detection (HPLC-ECD) is an attractive method with sensitivity and selectivity for the determination of redox compounds. However, an improper system makeup or operation is apt not to show such the intrinsic characteristics of the analytical results by HPLC-ECD in regards to biological sample assays. In this review, HPLC-ECD enabling high-sensitive and precise analysis of compounds of biological importance was developed using the following chemometric strategies: spectrum analysis of chromatographic baseline noise, standard deviation (S.D.) of area measurements in baseline noise from stochastic aspects, and optimization of HPLC conditions and method validations in HPLC-ECD using the prediction of precision based on the FUMI (Function of Mutual Information) theory. When HPLC-ECD was established using a capillary column (0.2 mm i.d.), catechins were determined at attomole levels and the present HPLC-ECD was applied to the determination of concentration profiles of catechins in human plasma after green tea ingestion. Moreover, two HPLC-ECD systems for determining acids and bases were developed by the means of the voltammetric reduction of quinone and the oxidation of trolox, respectively. Thus, the application of HPLC-ECD methods has been remarkably expanded through the development of novel ECD for the determination of acids and bases which are less active electrochemically. The present methods for determining acids and bases were applied to the pharmacokinetic studies of free fatty acids and theophylline, respectively. In conclusion, it was shown the present HPLC-ECD methods have been successfully applied to biomedical and pharmaceutical analyses.