A quarterhorse filly born in March was referred to the Iowa State University Veterinary Teaching Hospital with a two week history of respiratory problems. Symptomatic treatment with ampicillin, tribrissen, and amikacin had not resolved the problem. At the physical examination the filly was bright and alert. She had an elevated body temperature, 103.4F, a strong and increased pulse rate of 80 per minute and an increased respiratory rate of 64 per minute. Lung sounds were harsh in the dorsocaudal region and crackles and wheezes were heard vetrally.