Preprandial and postprandial plasma uric acid concentrations were evaluated in 12 healthy blackfooted penguins (Spheniscus demersus). Five male and 7 female penguins were fasted overnight, and blood was collected the next morning. Four days later, the same group of birds was given a morning feeding of fish ad libitum. Each bird's food consumption was recorded over a 2-hour feeding period. A blood sample was collected from each bird after removal of the fish (0- to 2-hour postprandial sample) and again 4 hours later (4- to 6-hour postprandial sample). Plasma samples were analyzed for uric acid and blood urea nitrogen (BUN) concentrations. In the 8 birds that consumed food during the 2-hour feeding period, plasma uric acid concentrations were significantly higher in both the 0- to 2-hour and 4- to 6-hour postprandial samples than in the preprandial samples. Uric acid concentrations were significantly lower in the 4- to 6-hour postprandial samples than in the 0- to 2-hour postprandial samples. Preprandial uric acid concentrations were <10 mg/dl, and 0- to 2-hour postprandial concentrations were >13.4 mg/dl (mean concentration = 21.2 mg/dl). No significant differences were found between preprandial and postprandial BUN concentrations. In penguins, uric acid concentrations must be measured after a fast to avoid a possible misdiagnosis of renal disease or gout.