Mice were exposed to chlorine and treated intramuscularly with vehicle or budesonide beginning 1 h after exposure, 1 day after exposure, or 2 days after exposure and treated for either 7, 6, or 5 days respectively. Lungs were collected for histological analysis 7 days after chlorine exposure. PSR staining was performed on tissue sections, and quantification of collagen staining was performed using ImageJ. a, p<0.01 vs other groups. b, p<0.05 vs unexposed. n=7–9 mice per group.