Serological evidence of infection with Babesia bovis and Babesia bigemina at a number of sites in Pemba was obtained using an enzyme-linked immunosorbent assay (ELISA) capable of detecting the appropriate parasite-specific antibody. Overall, 96% of animals were found to be positive for B. bovis, 88% were positive for B. bigemina and 88% were positive for both Babesia species. Antibody to B. bovis and B. bigemina was detected early in life in a number of calves born on Pemba, and was considered to be of maternal origin. The amount of maternal antibody in the serum of individual animals fell throughout the first 3 months of life. Later in life, antibody levels increased, probably in response to Babesia infection from natural tick challenge. These results suggest that infection with both Babesia parasites is widespread throughout Pemba and that both parasites probably exist in an enzootically stable situation.