A novel wall-jet cell with parallel dual cylinder (PDC) microelectrodes was constructed and used for flow injection analysis (FLA). The detector takes the advantages of "redox recycling" between bipotentiostated microcylinder electrodes (- 0.4 V/SCE and 0.0 V/SCE respectively) and shows high sensitivity and selectivity for riboflavin which is electrochemically reversible. In 0.1 mol 1(-1) NaHSO3 media and at a flow rate of 1.0 ml 1(-1), 56.8% collection efficiency was found at a PDC device with cylinder diameter of 20 mum and an interelectrode gap of 2 mum. With this device, the FIA peak current at collector electrode had a linear relationship with riboflavin concentration over a wide range (from 70 ng to 35 pg), and the detection limit was 35 pg (signal-to-noise ratio of 3). For 10 successive replicate injections of 35 ng and 3.5 ng of the analyte, relative standard deviations were 1.7% and 2.8% respectively. This method was applied to the direct determination of riboflavin (vitamin B2) in multivitamin tablets without the usual liquid chromatographic separation procedures and good results were obtained. The method proposed is simple, rapid and economic.