Immunogenic effect of the Lyssa and Lyssavac rabies vaccines were compared in sheep. Blood samples were collected 8 times from the experimental groups of 5 animals each during a 6-month period after vaccination. The dynamics of virus neutralizing antibodies was followed and the in vitro reactions of peripheral lymphocytes were studied. In the 3rd week after vaccination the titre of virus neutralizing antibodies was higher (1:128.4) in the experimental group immunized with the Lyssavac than in that immunized with the Lyssa vaccine (1:118) and it remained also at a higher level in the 6th month after vaccination (1:50) than that of the group immunized with the latter vaccine (1:20.4). As regards the in vitro reactions of lymphocytes, no essential differences were found either in the rates of immune rosette formation or in the degree of blastogenesis measured by the incorporation of /sup 3/HTdR. The mean values of IgG and IgM positive cells were also similar in both experimental groups as it was determined by immunofluorescence.