Cardiac troponin T (cTnT) is being increasingly used as a blood marker of acute or ongoing cardiac injury in various laboratory animals although the range of species in which it is applicable and its tissue selectivity has not been demonstrated. To address this concern, cardiac and skeletal muscle biopsy specimens from various species were homogenised and diluted, and their reactivity was then determined in the first- and second-generation immunoassays for cTnT. Cardiac tissue reactivity was found for all species studies, being highest for rats and several-fold lower for chickens and fish, and intermediate for dogs, pigs, goats, cows, sheep, horses, rabbits, and turkeys. Skeletal muscle had 10 per cent of the reactivity of cardiac muscle in the first-generation assay and 1 per cent of the reactivity of cardiac muscle in the second-generation assay. In the absence of moderate to marked skeletal muscle injury, the second-generation cTnT immunoassay has sufficient reactivity and tissue-selectivity to serve as a blood test for the discrimination between cardiac and skeletal muscle injury in a wide range of species.