A 3½-year-old male Shih Tzu dog was examined by a referring veterinarian at the University of Georgia Veterinary Medical Teaching Hospital, Athens, GA, for chronic exercise intolerance since 6 months of age and coughing of 4 months' duration. The dog's medical history included mild seborrhea sicca and seasonal atopic dermatitis, treated with dietary modification and parenteral triamcinolone injections every 2-3 months. The dog had been treated with a 2-week course of tetracycline (15 mg/kg PO q8h) 3 months before examination for lethargy, fever, and weakness in conjunction with high serum immunoglobulin G titers to Borrelia burgdorferi (1,024; reference range, Ͻ256) and Rickettsia rickettsii (128; reference range, Ͻ64). The dog also received amoxicillin and clavulanate (20 mg/ kg PO q12h) for 10 days 4 months before referral and enrofloxacin (5 mg/kg, PO q12h) for 10 days 7 weeks before referral. No improvement was seen with any of these therapies. Hematologic abnormalities present during this time included a persistent neutrophilic leukocytosis with an inconsistent lymphocytosis and eosinophilia.At the time of referral, examination revealed the dog to be bright, alert, and responsive. Rectal temperature was slightly high (102.8ЊF [39.3ЊC]; reference range, 99.5-102.5ЊF [37.5-39.2ЊC]). The dog had a normal pulse rate (130 beats/min; reference range, 110-130 beats/min) and increases in respiratory rate (50 breaths/min; reference range, 15-30 breaths/min). Lung sounds were increased in intensity, and the dog had an easily induced dry, hacking cough.Abnormalities on hematologic testing included a leukocytosis (23.4 ϫ 10 3 cells/L; reference range, 5.1-13.0 cells/L) with a mature neutrophilia (18.3 ϫ 10 3 cells/L; reference range, 2.9-12.0 cells/L) and eosinophilia (2.1 ϫ 10 3 cells/L; reference range, 0.0-1.3 cells/L). Serum total protein (7.6 g/dL; reference range, 5.4-7.5 g/dL) and globulin concentrations (4.2 g/dL; reference range, 1.9-5.3 g/dL) were increased. Urinalysis was within normal limits. Fundic examination revealed no abnormalities. An interstitial lung pattern was seen on thoracic radiographs ( Fig 1A,B). No parasite ova were seen in feces examined by Sheather flotation or Baermann extraction. Cytologic findings of a transtracheal washing were of a moderate amount