Highly sensitive analytical methods of various biological substances developed in the author's laboratory are reviewed. Amino sugarsand amino acids are determined by a fluorophotometric method using pyridoxal-Zn(II) ion. α-Oxo acids are also assayed fluorophotometrically with pyridoxamine-Zn(II) ion. Various oxosteroids are assayed by fluorescence high-performance liquid chromatography using dansyl hydrazine as a pre-labeling reagent. Bile acids are also determined fluorophotometrically with highperformance liquid chromatography after labeling with 1-bromoacetylpyrene. Fluorescence and chemiluminescence reactions are applied to enzyme immunoassays of various hormones and drugs.