A precise, simple and rapid method is described for the determination of inorganic arsenic [As(iii)+As(v)] in seafood products. The inorganic species were isolated from the matrix by microwave-assisted distillation and determined by hydride generation atomic absorption spectrometry (HGAAS). The microwave and chemical parameters were optimized in order to obtain quantitative inorganic arsenic recoveries. The analytical features of the method are as follows: detection limit 10 ng g(-1) (dry mass) or 2 ng g(-1) (fresh mass); precision (RSD) 4%; recoveries 106 +/- 3% for As(iii) and 113 +/- 4% for As(v). Under the optimized conditions, arsenobetaine, arsenocholine and tetramethylarsonium ion added to samples of seafood were not distilled; however, minor species were distilled and were detected in various percentages: 109% monomethylarsonic acid; 11% dimethylarsinic acid; 0.2% trimethylarsine oxide. The concentrations expressed as arsenic contributed by these species would imply a mean overestimate of inorganic arsenic of about 24 ng g(-1) dry mass (dm). The concentrations of inorganic arsenic found in natural seafood samples ranged between 0.053 and 1.145 mu g g(-1) (dm) (mean moisture content 78%). The procedure was compared with an alternative methodology in which acid digestion-solvent extraction-HGAAS was used for the determination of inorganic arsenic. A Student's t-test for paired samples of the data obtained by the two methodologies showed no significant differences (P -value 0.66).Comisio´n Interministerial de Cienc´ıa y Tecnolog´ıa (CICyT), Project ALI96–0511