Concentrations of mercury (Hg) in swordfish (Xiphias gladius) present a food safety problem for many countries. This study analyses total Hg (t-Hg) concentrations in 27 samples of swordfish marketed in Spain in 2005 and in their bioaccessible fractions (soluble concentration in gastrointestinal medium), obtained after applying an in vitro digestion method. Methylmercury (MeHg) was also determined in the bioaccessible fractions. t-Hg concentrations in the samples were 0.41-2.11 mg kg(-1) wet weight, with a mean of 0.96 +/- 0.47 mg kg(-1) wet weight. A total of 37% of the samples exceeded the Hg limit set by Spanish legislation (1.0 mg kg(-1) wet weight). Bioaccessible t-Hg concentrations were 0.17-1.72 mg kg(-1) wet weight (0.63 +/- 0.4 mg kg(-1) wet weight), corresponding to 38-83% (64% +/- 14%) of t-Hg. Bioaccessible MeHg concentrations, representing 94% of the bioaccessible t-Hg concentrations, were 0.16-1.53 mg kg(-1) wet weight, with a mean of 0.49 +/- 0.32 mg kg(-1) wet weight. Children and adults who regularly consume this product in Spain have Hg and MeHg intakes that exceed the tolerable daily intake limits recommended by the Food and Agricultural Organization/World Health Organization (FAO/WHO) and US Environmental Protection Agency (USEPA). These results show the need for recommendations about swordfish consumption by population groups at risk in Spain.