In the present study, a selection experiment for antibody (Ab) titer against SRBC in chickens was analyzed. Two lines were divergently selected for increased and decreased Ab titer. Further, a randombred control line, originating from the same base population, was included in the experiment. The heritability for immune response against SRBC was estimated after 18 generations of selection. In total, Ab titers obtained from 16,459 chickens were included in the analysis. Data was analyzed using an animal model. Posterior distributions for variance components and heritability were obtained using Markov Chain Monte Carlo methods. Response to selection was evaluated by constructing the posterior distribution for the genetic trend. In addition, a bivariate animal model was used in which male and female antibody titers were treated as different traits to estimate correlations between male and female immune response against SRBC. The heritability of Ab titer response, when using information from all three lines, was 0.18. The 90% highest posterior density region for the estimated heritability ranged from 0.16 to 0.19. In Generation 18, the genetic difference between the high and the low line was 5.1 phenotypic standard deviations. Analyses of each line separately revealed large differences in heritabilities between the lines, which could be mainly attributed to differences in error variances between the lines. The results suggest that selection for high Ab titers cause an increased environmental sensitivity. The estimated genetic correlation between male and female Ab titer was 0.92 and was not significantly different from 1.