The aim of this study was to evidence acute phase response in bronchoalveolar lavage fluids (BALF) from calves with bronchopneumonia by measuring Haptoglobin and Serum Amyloid A (SAA) concentrations and some enzyme activities. For that, 30 calves with bronchopneumonia and 8 clinically healthy calves were selected on the basis of the clinical signs and examination and laboratory analysis. Haematological analysis (White Blood Cell counts) was performed using an automated haematology cell counter. In blood and BALF samples, gamma-glutamyl transferase (GGT), lactate dehydrogenase (LDH) and alkaline phosphatase (ALP) activities and the total protein concentrations were measured using an automatic analyzer, whereas Haptoglobin and SAA concentrations were measured with commercially available ELISA kits. Proteinemia, GGT activity, haptoglobin and SAA concentrations in sera from diseased calves were significantly and dramatically increased compared to the healthy controls, while increases in other parameters (leukocyte count, ALP and LDH activities) were not statistically significant. Significant increases in LDH and GGT activities and in concentrations of the 2 acute phase proteins were also evidenced in BALF samples from calves with bronchopneumonia compared to the controls. In addition, except in 2 diseased animals, haptoglobin and SAA concentrations in BALF samples were above 250 and 25 mu g/L, respectively, whereas they have remained below the threshold values in all clinically healthy calves. These results show that BALF haptoglobin and SAA concentrations are useful acute phase proteins (APPs) for the determination of pulmonary inflammation in calves and future studies are needed to determine the importance of local acute phase response in the respiratory system.