Fever following fiberoptic bronchoscopy occurs in 10-25% of the patients and its origin is not well understood. We prospectively examined changes in body temperature (T degrees), mean systemic arterial pressure (MAP) and oxygenation after 2 bronchoalveolar lavages (BAL, bronchoscopic and non-bronchoscopic) for 34 procedures in 25 intubated patients. In patients with pneumonia (11 investigations) we observed a rise in T degrees 3 h after bronchoscopic and non-bronchoscopic BAL, p less than 0.0001, a decrease in MAP, p = 0.008 and arterial oxygenation, p = 0.002. Of patients with pneumonia 73% had a rise in T degrees of more than 1 degrees C compared with only 17% of those without pneumonia (p = 0.005). Patients without pneumonia (23 procedures) had no significant changes in T degrees, MAP and arterial oxygenation following the 2 BAL procedures. Changes in T degrees correlated significantly with those in MAP, and with the level of endotoxin in bronchoscopic BAL fluid. These findings suggest that BAL in patients with pneumonia may cause intravascular translocation of toxins or mediators producing pyrogenic and hypotensive effects.