Abnormalities have been previously noted in the lipid content of the lavage fluid of patients with bacterial pneumonia. In order to determine if these changes were also seen in surfactant apoproteins, we studied levels of surfactant protein A (SP-A) in patients with bacterial pneumonia. Patients without human immunodeficiency virus who were being evaluated for pulmonary infiltrates underwent bronchoscopy with bronchoalveolar lavage (BAL). Twenty-two patients with pneumonia, 12 caused by gram-positive organisms (Gm+ PNEU) and 10 caused by gram-negative organisms (Gm- PNEU), were compared with 10 patients with idiopathic pulmonary fibrosis (IPF) and 11 control subjects (CON). The percentage of neutrophils in the BAL was significantly higher in the patients with IPF and the pneumonia groups than in the control group (CON: mean, 1; range, 0 to 3. IPF: mean, 26; range, 13 to 42). Gm+ PNEU: mean, 33; range, 8 to 99. Gm- PNEU: mean, 64; range, 10 to 92; p < 0.0001). The amount of SP-A in the BAL fluid was similar for the CON and the IPF groups (CON: mean, 15; range, 5.75 to 26.5 micrograms/ml BAL. IPF: mean, 18.4; range, 6.49 to 45.64 micrograms/ml), whereas both pneumonia groups had significantly less SP-A (Gm- PNEU: mean, 5.54; range, 0.58 to 12.7. G+ PNEU: mean, 1.93; range, 0.47 to 6.74; p < 0.001). There was significantly less SP-A in the Gm+ PNEU group than in the Gm- PNEU group (p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)