A simple, sensitive and rapid flow-injection spectrophotometric method was developed for the determination of trace amounts of Au(III) in aqueous dimethylformamide (DMF). The method is based on formation of Au(III)-(3,5-DMHAAINH)(3) complex. The optimum conditions for the chromogenic reaction of Au(III) with 3,5-DMHAAINH is studied and the colored (reddish brown) complex is selectively monitored at lambda(max) 490 nm at pH 6.0. The reaction and flow conditions of the full experimental design were optimized. The detection limit (2 s) of 0.1 mu g l(-1) Au(III) was obtained at a sampling rate of 15 samples h(-1). Beer's law is obeyed over the range of 0.30-4.00 mu g ml(-1). The molar absorptivity and Sandell's sensitivity were 3.450 x 10(4) M and 0.0050 mu g ml(-1), respectively. Job's method of continuous variation and stability constants corresponding to these maxima was determined and found to be 9.3 x 10(15) (1:3, M:R) (M, metal; R, reagent). The detailed study of various interferences confirmed the high selectivity of the developed method. The method was successfully applied for the determination of trace amount of Au(III) in water and pharmaceutical samples. The results obtained were in agreement with the reported methods at the 95% confidence level. (c) 2004 Elsevier B.V. All rights reserved.