Babesiais spread to humans via ticks or blood transfusions. Severity ofPlasmodium falciparummalaria is strongly correlated to the ABO blood group of the patient.Babesia divergensis an intraerythrocytic parasite with many similarities to malaria, but the impact of ABO on the susceptibility to and progression of the infection in humans is unknown. We have now culturedB. divergensin human group A, B and O erythrocytes in vitro and measured rates of multiplication. The predilection for the different erythrocyte types was also determined using an in vitro erythrocyte preference assay when the parasites were grown in group A, B or O erythrocytes over time and then offered to invade differently stained erythrocytes of all the blood types at the same time. The results showed no difference in multiplication rates for the different blood types, and the parasite exhibited no obvious morphological differences in the different blood types. When cultured first in one blood type and then offered to grow in the others, the preference assay showed that there was no difference between the A, B or O blood groups. In conclusion, this indicates that individuals of the different ABO blood types are likely to be equally susceptible toB. divergensinfections.