The article examines the cause of megaesophagus in the parma wallaby, Macropus parma, at the San Diego Zoo in California. It involves restrospective and prospective studies at the zoo and a multi-institutional survey in the U.S. An etiology of the disease is not identified through the restrospective study and the presence of the disease and severely delayed esophageal transit time are detected in the animals through the prospective study. The assumed causes of megaesophagus such as myasthenia gravis, lead toxicosis, and toxoplasmosis are eliminated.