Background: The purpose of this study was to determine serum reference values for creatine kinase (CK), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) in captive-born and wild-caught owl monkeys to assess their usefulness for diagnosing myocardial disease. Methods: Blood samples were collected for CK, AST and LDH determinations. In addition, urine samples were collected and semiquantitative tests performed. Results: There was no statistically significant difference between CK, AST and LDH when comparing both groups. However, when comparing monkeys with proteinuria to those without proteinuria, a statistically significant difference in CK value was observed (P=0.021). In addition the CK/AST ratio revealed that 29% of the animals included in this study had values suggesting cardiac infarction. Grossly, cardiac concentric hypertrophy of the left ventricle and small, pitted kidneys were the most common findings. Microscopically, myocardial fibrosis, contraction band necrosis, hypertrophy and hyperplasia of coronary arteries, medium-sized renal arteries and afferent glomerular arteriolae were the most significant lesions, along with increased mesangial matrix and hypercellularity of glomeruli, Bowman's capsule and peritubular space fibroplasia. Conclusions: These findings suggest that CK, AST and LDH along with urinalysis provide a reliable method for diagnosing cardiomyopathies in the owl monkey. In addition, CK/AST ratio, proteinuria and the observed histological and ultrastructural changes suggest that Aotus vociferans suffer from arterial hypertension and chronic myocardial infarction. © Journal compilation © 2008 Blackwell Munksgaard.