A field trial was performed to determine the effect of a trivalent vaccine on Clinical Respiratory Tract Problems (CRTP) in veal calves. The vaccine has been developed to increase immunity against the causal agents of IBR, BVD and BRSV infection. In total 928 calves, housed in 16 compartments of one herd, were involved. In four compartments of 58 calves each, vaccinated and non-vaccinated calves were housed together. Four other compartments were treated as a whole and 8 compartments were left untreated. CRTP incidence, medications, weight gain, haemoglobulin and IgG level were recorded. From CRTP positive animals, seroconversion and presence of specific bacteriae and/or viruses were measured as well. Results of the compartments where vaccinated and non-vaccinated calves were housed together showed that the incidence of CRTP in vaccinated calves was 0.16 while it amounted to 0.28 in controls. Most cases were found between day 40 and 60 after the start of the trial. Seroconversion for vaccine specific viruses was sporadically found, but the presence of Pasteurella's was confirmed in the majority of cases. Presumably, the higher incidence of CRTP in the control group was due to a higher level of BVDV infection which might facilitate a clinical infection with Pasteurella's. Vaccination was also negatively related to the percentage of affected lungs at slaughter, the number of days antibiotics had to be administered and subsequently to medicine costs, although these effects were not significant. Daily weight gain was significantly affected by CRTP, but not by vaccination. The effects of vaccination in the compartments where calves were either all vaccinated or not-vaccinated, were similar or larger when compared to the effects in compartments where half of the calves were vaccinated.