A new, sensitive and selective spectrofluorimetric method has been developed for the determination of duloxetine (DLX) in capsule and spiked human plasma. DLX, as a secondary amine compound, reacts with 7-chloro-4-nitrobenzofurazon (NBD-Cl), a highly sensitive fluorogenic and chromogenic reagent used in many investigations. The method is based on the reaction between the drug and NBD-Cl in borate buffer at pH8.5 to yield a highly fluorescent derivative that is measured at 523nm after excitation at 478nm. The fluorescence intensity was directly proportional to the concentration over the range 50-250ng/mL. The reaction product was also measured spectrophotometrically. The relation between the absorbance at 478nm and the concentration is rectilinear over the range 1.0-12.0 mu g/mL. The methods were successfully applied for the determination of this drug in pharmaceutical dosage form. The spectrofluorimetric method was also successfully applied to the determination of duloxetine in spiked human plasma. The suggested procedures could be used for the determination of DLX in pure form, capsules and human plasma being sensitive, simple and selective. Copyright (c) 2014 John Wiley & Sons, Ltd.