An injection of anti-rat erythrocyte rabbit serum or its 7S globulin fraction into rats resulted in immunohemolytic anemia associated with a positive antigloublin test examined with anti-rabbit gammaglobulin serum. However, an injection of 19S globulin fraction from the antierythrocyte serum failed to cause immunohemolytic anemia, although it induced a transient decrease in red cell count. These results indicate that 7S antibodies are responsible for the induction of antiglobulin test positive, experimental immunohemolytic anemia. The ferrokinetic and stathmokinetic studies revealed the prolongation of generation time of basophilic and polychromatic erythroblasts in rats injected with anti-erythrocyte serum or its 7S globulin fraction. The results from in vitro [³H]thymidine incorporation experiments also confirmed this prolongation. The analysis of in vivo [³H]thymidine labeling of erythroblasts in rats which were given the 7S globulin antibodies suggested the prolongation of the G₁ time of the erythroblasts. These results suggest that the effects of anti-erythrocyte antibodies on the generation cycle of erythroblasts are to prolong their G₁ time and keep them dormant.