BALB/c mice immunized agaimt Babesia rodhaini for two months showed peak parasitemia of9. I 3 ± 6.35 and 5. I ± 5.98 at 7 and 9 days post-challenge. Mice, however, immunized for ten months at 9 days post-challenge exhibited a lower peak parasitemia of3. 04 ±5. 84. Similarly, Babesia microti-immunized mice challenged with B. rodhaini exhibited a significantly lower peak parasitemia of I. 02± 0. 76. Comparison of parasite components between B. rodhaini and B. microti using polyspecific sera revealed several shared or common parasite components of mokcular weights 62, 55, 45-47. 30-31 and 26-28 kilodaltom. The presence of several shared/common parasite antigens in Babesia rodhaini and Babesia microti may account for the cross-immunity noted in this study.