Mercury (Hg) is a global environmental contaminant that affects ecosystems. It is known to biomagnify through food webs, and to bioaccumulate especially in the tissues of top predators. Large scale comparisons between taxa and geographic areas are needed to reveal critical trends related to Hg contamination and its deleterious effects on wildlife. Yet, the large variety of tissues (keratinized tissues, internal organs, blood) as well as the variability in the units used to express Hg concentrations (either in wet- or dry-tissue weight) limits straightforward comparisons between studies. In the present study, we assessed the moisture content that could influence the total Hg (THg) concentrations measured in several tissues (claws, scutes, total blood and red blood cells) of three caiman species. First, we aimed to evaluate the moisture content from the different tissues, and second to provide information on THg concentrations in various matrices. Our results show a difference of THg concentrations between the tissues and intra- and interspecific variations of moisture content, with the highest THg values found in keratinized tissues (scute keratinized layers and claws). For the three species, we found positive relationships between body size and THg concentration in keratinized tissues. In the blood, the relationship between body size and THg concentration was species-dependent. Our results emphasize the need for a standardized evaluation of THg concentration and trace elements quantification based on dry weight analytical procedures. In addition, the use of both blood and keratinized tissues offers the possibility to quantify different time scales of THg exposure by non-lethal sampling.