Data collected from a longitudinal survey carried out over a 2-year period, in four dairy herds in western France, were used to assess Babesia divergens antibody kinetics. Farms were visited once a month. The total number of animals monitored was 236 including calves, heifers and cows of the Holstein and Normande breeds. An ELISA was used to follow the humoral response levels against Babesia divergens. When the study began, in the autumn of 1991 (200 animals), half of the animals were already seropositive (57.5%). In all four herds, the percentage of positive animals decreased during winter, and increased during spring. Antibody levels remained stable in 49 animals, high for some, very low or negative for others. Most seropositive animals showed at least one antibody peak at some time during the 2-year period, but some presented two to five. Among the calves, 61.3% showed seroconversion during the first pasture season. Similarly, 60% of the newly purchased cows showed increases in antibody levels during the 3 months after their introduction into a new herd, regardless of the initial antibody level. Only three dairy cows had expressed a clinical babesiosis, these cows were already seropositive. Clinical incidence is low in the four farms, nevertheless serological prevalence and incidence are high.