The association between selection for body weight and immune responsiveness was studied in Japanese quail and White Plymouth Rock chicken populations. Quail populations consisted of a randombred control (C) line and a line selected for high (HW) 28-day body weight. The chicken populations used were lines selected for high (HW) and low (LW) 56-day body weight, reciprocal Fi crosses (HL and LH), and F2 crosses of the Fi (HLHL and LHLH). Kinetics of primary and secondary antibody response to SRBC antigen was examined in Line C quail (Experiment 1). At most times post-primary inoculation (PPI), antibody titers were highest for antigen concentration 2.5%. The presence of MER antibodies was very low PPI, but increased following reinjection. Primary antibody response was then compared between C line and HW line of quail (Experiment 2). Antigen concentration 2.5% once again resulted in the highest titers. Line HW quail were less able to maintain high antibody titer levels to SRBC antigen than the randombred control line from which they originated. Mode of inheritance for immune responsiveness in selected populations of chickens and crosses between them was examined (Experiment 3). Additive genetic variation was important in the inheritance of both primary and secondary responses to this antigen. Reciprocal differences and heterosis of the F₁ crosses were also factors in the inheritance of secondary response. Kinetics of primary and secondary responses were evaluated in the parental weight lines and in lines of White Leghorn chickens divergently selected for antibody response to SRBC antigen. At all times PPI, line HA chickens had the highest antibody titers, while those from line LA consistently had the lowest titers. Lines HW and LW reacted similarly to line LA early in response, but showed higher peak levels later on. In both primary and secondary responses, the weight lines peaked at similar levels. Thereafter, line LW maintained a high antibody titer level to SRBC antigen than line HW. / Master of Science