Abstract Microhemagglutination procedures were used to quantify antibody titers against human erythrocytes and ovalbumin in calf sera. Calves were also monitored for the prevalence of pneumonia and diarrhea. Calves, 72 males and 82 females, were the progeny of 15 AI bulls. Blood was sampled weekly for 2 wk after primary and secondary immunizations. Antibody response peaks to both antigens occurred by 14 and 7 d postimmunization, respectively. There were significant effects of season and birth and location of rearing on antibody titers against both test antigens. Diarrhea prevalence was negatively associated with high primary response antibody titers against human erythrocytes, but no trends were observed for pneumonia prevalence and for antibody titers to ovalbumin. Paternal half-sib heritability estimates ranged from 0 to .40±.32 for primary antibody responses and from 0 to .87±.50 for secondary antibody responses, depending on antibody specificity, and those for average titer were higher for antiovalbumin antibody (h2 = .48±.39) than for antihuman erythrocyte antibody (h2 = .31±.21). Although the environmental component of the humoral immune response is substantial, heritabilities of the magnitude in this study suggest the feasibility for successful genetic manipulation of antibody response profiles of young calves, and these may contribute to enhanced disease resistance.