Six breeding groups of chickens, each characterized by a different haplotype of the B blood group system, were challenged with different classes of antigens, namely Newcastle disease vaccine (ND), infectious bronchitis vaccine (IB), infectious bursal disease viral agent (IBD), Salmonella pullorum antigen (P), and sheep red blood cells (SRBC). Parents were challenged at 20 weeks of age, and their offspring were challenged at 3 weeks of age. Blood samples were taken from the parents at 1 week after challenge, and from the offspring at 1, 2, 3, and 4 weeks after challenge for determination of antibody titers to each antigen. The offspring were also challenged at 8 weeks of age in the wing-web with Rous sarcoma virus (RSV). Tumor scores were taken weekly on individual chickens for the next 10 weeks. There were significant differences (P less than .01) between breeding groups of parents for antibody titer responses to ND, IB, P, and SRBC. There were significant differences (P less than .05) between the breeding groups of offspring for antibody titer responses to ND, IB, IBD, P, and SRBC. There were significant (P less than .01) differences between the breeding groups in the accumulative tumor scores over the 10-week period. The lines that cause regression of Rous sarcomas (R-lines) were significantly (P less than .01) superior in resisting tumor growth to those lines that allow progressive growth of tumors (Pr-lines). The only antigen to which the R-lines gave significantly (P less than .01) higher titers of antibody responses than the Pr-lines was SRBC.