A sensitive and simple fluorometric method for the determination of N, N'-bis(2-aminoethyl)-1, 2-ethanediamine dihydrochloride (triethylenetetramine) in human plasma by high-performance liquid chromatography is described. Free triethylenetetramine (TETA) obtained by passing the TETA-copper clelate compound through a solid-phase cation exchange resin was converted to its fluorescamine derivative in the presence of ethylenediaminetetraacetic acid to mask the interfering metal ions in the reactin solution, and the derivatives were separated on a nitrile high-performance liquid chromatograph column (Nucleosil 5-CN) using isocratic elution. The plasma levels of TETA were measured in eight patients receiving treatment for excess copper. Absorption rates of TETA were relatively slow and the peak levels were significantly different among patients. The bioavailability of TETA in the rat was also examined and the ratio of intestinal absorption was extremely low.