The objective of this study was to determine the effect of supplemental dietary chromium (Cr) on antibody responses of feedlot calves. Fifty-five newly weaned calves were divided into two groups, 28 that received supplemental Cr and 27 that did not, and were immunized with a commercial vaccine against bovine infectious rhinotracheitis virus (IBR) and bovine parainfluenza virus type 3(PI-3). Sera harvested from blood sampled preimmunization, and at days 14 and 28 postimmunization (PI), were assayed for anti-IBR and anti-PI-3 antibody titers. Individual calves were also scored as seroconverters if day 14 or 28 PI titers were > or = 3 times the value of the preimmunization titer. Thirty-five calves did not seroconvert to either antigen. Of 20 IBR seroconverters, 15 calves were from the Cr-supplemented group while only five calves were controls (p = 0.007). There was no treatment difference in the number of PI-3 seroconverters. Least squares analysis of actual antibody titers revealed that Cr supplementation increased the magnitude of the peak antibody response to the IBR (p = 0.003), but had no effect on anti-PI-3 antibody titers. These data confirmed and extended our previous observations that supplemental Cr can be immunomodulatory in cattle.