In a research of chromium availability, the three-stage sequential extraction procedure, proposed by European Community Bureau of Reference (BCR), has been applied for the metal fractionation in marine sediment samples. The procedure has been modified, evaluating the effect of microwave energy to perform the sequential method. Results achieved a substantial reduction in time in comparison to the traditional shaking technique. The time of the first and the second extractions were reduced to 30s in both steps using microwave heating and working at 66W of power. To the third extraction, higher power was necessary so it was chosen to work at 198W. In the last step investigated, time was reduced to 1min, being a great improvement respect to the conventional BCR sequential extraction protocol. Chromium determinations in these extracts were carried out by Electrothermal Atomic Absorption Spectrometry (ETAAS). The developed method was applied for chromium determination in marine sediment samples from Ria de Arousa (Galicia, NW of Spain). The values obtained by our laboratory ranged from 0.10 to 1.02mugg(-1) for soluble and reducible fractions, and from 5.5 to 60.0mugg(-1) for the oxidisable fraction. The higher concentrations obtained were the chromium associated with the organic fraction of the marine sediments.