Interleukin-8 (IL-8) is a potent neutrophil chemoattractant and activator. Pneumocystis carinii pneumonia is associated with an accumulation of neutrophils in bronchoalveolar lavage (BAL) fluid. Thus, we hypothesized that IL-8 is involved in the pathogenesis of P. carinii pneumonia. BAL fluid and serum were prospectively collected in 76 consecutive HIV-infected patients with a primary episode of P. carinii pneumonia, as well as in 10 healthy control subjects. Patients were found to have elevated levels of IL-8 in BAL fluid compared with control subjects (p < 0.01). Nine patients died during the course of P. carinii pneumonia. Comparing survivors with nonsurvivors, the median IL-8 level in BAL fluid was 127 (0 to 3,900) versus 584 (127 to 6,100) pg/ml (p < 0.05). Furthermore, patients with levels of IL-8 in BAL fluid greater than 90 pg/ml (i.e., greater than control subjects) had significantly worse vital prognosis (log rank test, p < 0.05). Thirteen percent required mechanical ventilation (MV). Patients requiring MV had a median IL-8 level of 396 (25 to 6,100) versus 129 (0 to 3,900) pg/ml for patients not requiring MV (p < 0.05). In conclusion: i) IL-8 in BAL fluid correlates to the clinical severity of the pneumonia, and ii) is a predictor of mortality and severe respiratory compromise.