Female Glossina morsitans morsitans maintained on rabbits previously immunized with whole tsetse body (WTB), engorged tsetse guts (ETG) or gravid tsetse uteri (GTU) for three successive generations showed no increase in mortality. However, a decrease in fecundity which varied with the tissue used as antigen and with the fly generation, was observed. During the three successive fly generations lasting about 4 months, the total decrease in fecundity was approximately 53, 59 and 70% for WTB, ETG and GTU respectively. The total increase in pupal mortality during the first two generations was approximately 7, 19 and 10% for WTB, ETG and GTU respectively, while the corresponding decreases in mean pupal weights were approximately 12, 8 and 11%. Flies fed on rabbits immunized with tsetse salivary glands (TSG), unfed tsetse guts (UTG) and protein extracted from gravid tsetse uteri (GTUP) showed a decrease in fecundity of 20, 26 and 31% respectively during the first fly generation, and a decrease in mean pupal weights of 6, 3 and 8%, while pupal mortalities increased by 38, 26 and 16% respectively.