Total mercury (T-Hg) and methylmercury (MeHg) concentrations have been measured in the muscle tissue of 16 fish species consumed in the Mojana region of Colombia. T-Hg analysis was performed by cold-vapor atomic-absorption spectroscopy (CV-ASS) and MeHg analysis by gas chromatography with electron-capture detection. Higher T-Hg and MeHg concentrations were detected in carnivorous species (T-Hg = 0.371 +/- 0.172 (microg g(-1) fresh wt, MeHg = 0.346 +/- 0.171 microg g(-1) fresh wt) than in non-carnivorous fish (T-Hg = 0.155 +/- 0.108 microg g(-1) fresh wt, MeHg = 0.146 +/- 0.102 microg g(-1) fresh wt). In the different species mercury was present almost completely as the methylated form, with percentages between 80.5 and 98.1% (mean 92.0 +/- 3.4%). In 13.5% of fish-tissue samples T-Hg concentrations exceeded the maximum level recommended by the World Health Organization for human consumption (Hg = 0.5 microg g(-1) fresh wt). Although mean T-Hg concentrations in all fish samples (0.269 +/- 0.181 microg g(-1) fresh wt) did not exceed this limit, risk assessment suggested that the consumption of 0.12 kg fish day(-1) could increase the risk of mercury poisoning of the inhabitants of this region.