Immune and oxidative parameters were evaluated as indicators of the influence of stress on the occurrence of respiratory syndrome in feedlot calves. The study was carried out on 60 2 and a half-month-old Simmentaler calves transported at feedlot. Mean daily feed consumption, daily weight gain, and behavioural activity were evaluated. Blood was collected on days 1, 3, 7, 14, 21, and 28 of feedlot. Serum NO ions, lipid peroxidation, acute phase proteins, IgG, and IgM were determined. The calves showed a decrease in feed consumption during the first 7 d of the feedlot. Sporadic stereotypies were noted. NO concentration showed a significant (P < 0.05) increase on days 7 and 14. Concentration of thiobarbituric acid reactive substances (TBARS) increased (P < 0.05) on days 1 and 3. IgM concentration was found to be considerably lower on days 14 and 28. Serum haptoglobin level showed a significant increase in stressed calves on days 1, 3, 7, and 14 of the feedlot. Based on these results, it can be suggested that stressors associated with transport and adaptation to the feedlot induce a stress reaction in calves, resulting in behavioural disorders, reduced weight gain, suppression of the humoral immunity and increased morbidity during the first weeks. These parameters seem to be crucial in evaluating the animals' health and welfare.