A rapid and sensitive AAS method is described for the determination of copper, cadmium and lead based upon on-line preconcentration on a microcolumn packed with C18material. These heavy metals are complexed with dithizone from ammonical solutions in the flow injection system and adsorbed on the column. The preconcentrated species were eluted with acidified methanol (pH ≥ 2) and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The retention efficiency was better than 98% resulting in sensitivity enhancement factors of 80, 90 and 60 for 10 ml sample containing copper, cadmium and lead, respectively. The respective detection limits are 1.2, 0.6 and 3.0 ppb for copper, cadmium and lead. The throughput of the samples was found to be 30/h, with a loading time of 1 min. The method has been applied to the analysis of marine sediment samples.