Mercury concentrations in carapace fragments of the green turtle Chelonia mydas from the Ceará coast in NE Brazil are reported. Concentrations varied from <0.34 to 856.6 ng.g(-1) d.w., and were highest (average of 154.8 ng.g(-1) d.w.) in juveniles (n = 22), whereas lowest concentrations (average of 2.5 ng.g(-1) d.w.) were observed in adult/sub-adult animals (n = 3). There was a significant negative correlation between animal size and Hg concentration probably due to different diets between juveniles and sub-adults/adults. Carapace fragments, which are non-invasive, non-lethal substrates, may be of importance for monitoring purposes of these generally endangered species.