A simple system for simultaneous fluorescence detection of primary and secondary amines has been developed. The optimum conditions for fluorescing secondary amines in the two-stage reaction technique using sodium hypochlorite and o-phthalaldehyde have been studied, and then the switching flow method (sodium hypochlorite is added only to secondary amines) and the non-switching flow method (sodium hypochlorite is added to all the amino acids) have been compared. It was concluded that the non-switching flow method ensures high efficiency and reliability. This newly-developed system was applied to the detection of amino acids and gave satisfactory results.