Iron(III) N,N'-bis(salicylidene)ethylenediamine (denoted as Fe(Salen)(+)) was prepared and characterized for its application in chemical analysis. From the stability constant of Fe(III)(Salen)(+) (7.1 x 10(25) M-1) and the formal, potentials of Fe3+/2+ and Fe(Salen)(+/o), the stability constant of Fe(II)(Salen) was calculated to be 3 x 10(17) M-1. This relatively weaker stability constant, compared with that of Fe(III)(Salen)(+), led to the occurrence of the electron transfer reactions between Fe(Salen) and electron acceptors, like oxygen and H2O2. Experimental results supported this hypothesis, showing that the pseudo-first order rate constants for the reactions of Fe(II)(Salen) with O-2 (DMSO-H2O, v/v 4:1) and H2O2 (pH 7) are 330 and 4400 M-1 s(-1), respectively. Because of this catalytic effect, a sensing electrode for glucose or uric acid was constructed on the basis of Fe(Salen)(+) and glucose oxidase (GOx) or uricase (UOx). According to the flow injection analysis (FIA), the detection limits were 1 mu M for glucose at pH 7 and 0.1 mu M for uric acid at pH 8.5, respectively. The linear response to each substrate covered a region of 1 mu M-10 mM for glucose and 5-40 mu M for uric acid. Fe(Salen)(+) might form a 1:1 adduct with beta-cyclodextrin (beta-CDx); the equilibrium constant was determined to be about 6 M-1. Although this chemical equilibrium, in terms of the numerical value, was not significant, the formation of (Fe(Salen)}(2)O was effectively limited as beta-CDx was incorporated.