Serum concentrations of the enzymes creatine kinase (CK) and aspartate aminotransferase (AST) were measured in captive and wild mallards (Anas platyrhynchos) as indicators of muscle damage. Baseline values for both enzymes were determined from six captive male mallards. During winter 1990 to 1991, six diets (including controls) representative of food available in the Mississippi alluvial valley were fed to captive female mallards housed in an outdoor aviary at the White River National Wildlife Refuge, Arkansas County, Arkansas (USA). Controlled handling of penned mallards resulted in elevated serum CK (means = 1,352 IU/liter; SD = 1,212) and AST (means = 101 IU/liter; SD = 95) concentrations consistent with myopathies. These serum enzyme elevations were not affected (P > 0.3) by dietary selenium concentrations in the six diets or by energy malnutrition suffered by birds fed soybeans. Capture of wild mallards with an entanglement type rocket net resulted in serum CK and AST concentrations (means = 12,035 and 330 IU/liter; SD = 8,125 and 171, respectively) that were higher (P < 0.001) than those reported after capture with an enveloping type rocket net. Baseline values, controlled handling values, and entanglement rocket net values for serum CK and AST all differed (P < 0.0001).