Abstract: In the cited FIA - AAS system (details and diagram given) dimethoxydithiophosphate (I) was shaken with 0.01 M nitric acid, CHCl3 and an excess of Cu for 2 min. The organic extract was decanted, the Cu(I)2 complex formed was extracted (x 2) into CHCl3 and Cu was continuously back-extracted into 0.2 M NH4+ - NH3 buffer (pH 10). The extract was injected into a carrier stream of water and Cu was determined by AAS at 324.8 nm. The detection limit was 0.39 ppm of I with a coefficient of variation (n = 9) of 1.6%. Results were comparable to those obtained by standard methods. Interference from Fe and Bi was eliminated by adding an excess of Cu; some thiophosphate pesticides interfered. The method was applied in the determination of malathion in an agricultural formulation.