The homeward journey began on a passenger train in a public compartment that was intermittently permeated with tobacco smoke. Several hours after boarding the train the infant awoke crying with a dry sounding cough. The infant had fed well just 45 minutes earlier. No formula was visible in the oropharynx either before or during the coughing episode. Tachypnea and respiratory distress gradually developed over the ensuing hour. On arrival at the emergency department dried blood was noted on the infant's lips; blood was suctioned from the mouth and posterior pharynx. The infant's respirations were 58/min, pulse oximeter saturation was 76% on room air, and subcostal retractions were present. Initial arterial blood gas levels measured PaCO2 of 46 mm Hg; pH, 7.19; and PaO2, 74 mm Hg on nasal cannula oxygen. Skin was mottled, cool, and pale. The heart rate was 183 beats per minute and rectal temperature 36.5°C. Tactile stimuli elicited a weak cry and withdrawal of extremities, but no eye opening. Orotracheal intubation was performed for increased work of breathing and desaturations by pulse oximeter. At the time of intubation bright red blood was oozing from the glottic opening. Chest roentgenogram revealed diffuse bilateral alveolar infiltrates. No bruising or rash was present. Initial laboratory results were as follows: hemogloblin, 123 g/L; hematocrit, 0.36; mean corpuscular volume, 910 g/L; platelets, 624 ×109/L; white blood cell count, 16 ×109/L; glucose, 10.4 mmol//L (187 mg/dL); serum sodium, 136 mmol/L; serum potassium, 6.4 mmol/L; serum bicarbonate, 21 mmol/L; serum urea nitrogen, 3.9 mmol/L (11 mg/dL); and serum creatinine, 35 µmol/L (0.4 mg/dL). Urine analysis showed no red blood cells, but proteinuria (1+); prothrombin time, 13 seconds (reference range, 11.0-12.6 seconds); partial thromboplastin time, 35.1 seconds (reference range, 27-39 seconds); and fibrinogen, 5058 µmol/L (reference range, 5882-11,764 µmol/L). Ampicillin and cefotaxime sodium were administered prior to the infant's being transferred to the tertiary care hospital. At arrival to the pediatric intensive care unit the infant's weight was 4.04 kg (reference range, 10%-25% percentile); length, 54 cm (reference range, 10%-25% percentile); and head circumference 3 to 5 cm (reference range, 25%-50% percentile). Bright red blood was repeatedly suctioned from the endotracheal tube. Breath sounds were diffusely diminished without rales or ronchi. No clubbing was present. The patient's abdomen was soft without hepatosplenomegaly or other masses. At flexible bronchoscopy submucosal hemorrhage was visualized in several subsegmental bronchi and petechiae were diffusely present in more distal airways. No active bleeding was evident. Approximately 10% of macrophages recovered from bronchial lavage fluid contained small amounts of hemosiderin. Microscopic stains and cultures of the fluid were negative for bacteria (including acid-fast bacilli), virus, Pneumocystis carinii, fungi, Mycoplasma pneumonia, and Chlamydia pneumonia. Methylprednisolone was administered at a dose of 1 mg/kg every 6 hours. Approximately 4 hours after the initial blood samples were obtained, the hemogloblin level and hematocrit had decreased to 105 g/L and 0.30, respectively. Within 4 days mechanically assisted ventilation was discontinued. The infant was breathing room air 24 hours later. A second flexible bronchoscopy revealed normal mucosa and no blood in the airway following extubation. Prior to the infant's discharge from the hospital another laboratory investigation included a skeletal survey (no fractures as evidence of trauma), cardiac ultrasound (normal anatomy), milk precipitins (none detected), antiglomerular basement membrane antibody (<6 equivalent units [EU]/mL, with normal reference range <6 EU/mL), antistreptolysin antibody level (<6 Todd U), and a cyclosporin level (<25 ng/mL). As an outpatient, findings for antineutrophil cytoplasmic antibodies were reported to be "negative." During hospitalization formula feedings were changed to nonsoy and noncow-milk–based protein formulas and these were continued following discharge from the hospital. Oral steroid was weaned within 1 month of the infant's returning home. The infant is almost 2½ years old and has remained clinically healthy without clinical evidence of recurrent pulmonary hemorrhage or obstructive reversible airway disease.