A desert tortoise (Gopherus agassizii) was trapped underground without food or water for nearly 11 mo near Yucca Mountain, Nevada (USA). Physical abnormalities included weight loss, sunken eyes, and muscle atrophy. Biochemical abnormalities determined from blood sampling included marked azotemia and hyperosmolality, which were attributed largely to accumulation and retention of nitrogenous wastes. Moderate hypercholesterolemia, hypophosphatemia, and increased aspartate transaminase activity, and mild hyperchloremia, hypocalcemia, hyperbilirubinemia and anemia also were observed, compared with results obtained from other tortoises sampled at the same time. The lack of, or only mild, alterations in most laboratory data exemplified the high degree of physiological adaptation tortoises can undergo when deprived of food and water for a prolonged period.