Neutrophils, apart from their role in immunodefence, are also connected with lung injury, because of excessive release of enzymes such as elastase and myeloperoxidase (MPO), as well as nitric oxide (NO) generation. The purpose of this study was the relation between release of neutrophil products, acute phase proteins level (APP) and ascorbic acid (AA) concentration in the course of BRD in calves. The study was carried out on 10 healthy and 10 BRD calves. Neutrophil enzymes were assessed spectrophotometrically, NO level was determined by Griess reaction. Fibrinogen level was estimated by the heat precipitation method. Haptoglobin was assessed by the Owen’s method. AA analysis was done after reaction with dinitrophenyhydrazine. We estimated that elastase (71.97 ± 3.89%) and MPO (29.7 ± 5.88%) release from neutrophils isolated from BRD calves was significantly higher than from healthy animals (54.23 ± 5.66% and 19.18 ± 8.3%, respectively, p < 0.05). Moreover, our experiment revealed the positive correlation between secretory action of neutrophils and APP. We also observed that increased secretory action correlated negatively with plasma concentration of AA.