A simple and sensitive indirect spectrophotometric method is described for the determination of mimosine based on its reaction with diazotized sulfanilamide (DZSAM). DZSAM couples with N-(1-naphthyl)ethylenediamine (NEDA) forming a pink colored azodye, absorbing maximally at 540 nm (εmax=27 mM-1 cm-1). In the present method, mimosine was first reacted with known excess of DZSAM and the unreacted DZSAM was determined by coupling with NEDA. The reaction of mimosine with DZSAM proceeded optimally at neutral pH. The decrease in absorbance of the DZSAM-NEDA-coupled product obeyed Beer's law in the concentration range of 0.005-0.15 μg ml-1 of mimosine. The present method was applied to estimate mimosine in plant extracts containing lesser than 0.05 μg ml -1 with recovery at 99±0.41%. The method described is superior to other reported methods in terms of ease of adaptability and sensitivity. © 2003 Elsevier B.V. All rights reserved.