Because feed and water deprivation during marketing and transport of feedlot calves may reduce ruminal B vitamin synthesis at a time when calves are most susceptible to infectious agents, we studied the effect of B vitamin injections on infection and immunity in 12 6-mo-old beef steer calves (153 +/- 8 kg) that were weaned, limit-fed, and deprived of feed. Six calves were injected with B vitamins and ascorbic acid every 48 h for 28 d starting 2 wk before virus inoculation. All calves were infected with an attenuated strain of bovine herpesvirus type 1 (BHV-1) on d 0. From time of arrival (d -20) until the end of a 3-d period without food (d -6), calves lost 13.1% of their initial weight. However, they regained weight after re-feeding so that net weight loss was 7.7% for the 20-d period prior to infection. The stress/BHV-1 model resulted in a mild respiratory infection in all calves with no difference observed between treatment groups. Vitamin injections did not significantly affect virus and interferon titers in nasal secretions, or lymphocyte blastogenesis. However, the B vitamin treatment tended to increase serum IgG titers to BHV-1 on both d 14 (1,120 vs 550, P = .115) and d 28 (2,400 vs 1,830, P = .37) after infection. Averaged across d 14 and d 28, IgG titers tended to be higher (P < .09) for the calves receiving B vitamin injections, indicating that the humoral immune response was enhanced by B vitamin treatment. B vitamin status in stressed calves at the time of vaccination or disease challenge may affect the success of the immune response.