Surfactant protein B (SP-B) is known to promote surfactant phospholipid film formation and reduce surface tension. Native SP-B is a homodimer in which subunit association is stabilized via covalent linkage through cysteine 48. We hypothesized that loss of the intersubunit bridge would alter SP-B function and lead to increased inflammation in response to challenge by hyperoxia or endotoxin. Transgenic mice in which SP-B cysteine 48 was mutated to serine were generated and crossed into the SP-B(/) background. Wild-type mice and transgenic mice carrying a single copy (SP-Bmon⁺) or two copies (SP-Bmon⁺⁺) of the transgene were exposed to 95% O₂ for 3 days or intratracheally injected with 10 µg of endotoxin. Interleukin-1, major intrinsic protein 2, and interleukin-6 in lung homogenates after 3 days of hyperoxia were significantly higher (P < 0.001) in SP-Bmon⁺ mice than SP-Bmon⁺⁺ or wild-type mice. At 16 h after endotoxin injection, cytokines in lung tissues were higher in SP-Bmon⁺ mice compared with wild-type mice (P < 0.05). Consistent with prolonged recovery in SP-Bmon⁺ mice, the percentage of apoptotic cells in alveolar lavage was significantly lower in SP-Bmon⁺ mice than in SP-Bmon⁺⁺ and wild-type mice. Overall, increased inflammation in SP-Bmon⁺ mice was corrected to a large extent by increased gene dosage, indicating that formation of the intersubunit disulfide bridge is not critical for SP-B function.