Studies were carried out in which laboratory mice were subjected to sequential feedings by slow feeding Ornithodoros talaje (Guerín-Méneville) larvae to detect and characterize the host cellular response. After the first exposure, histological evidence showed a strong neutrophil infiltration at the site of attachment and feeding. By the third exposure, a marked shift to lymphocytes was noted in the mouse tissues using histological preparations of the feeding ticks. Lymphocyte proliferation tests also provided indirect evidence of a host lymphocyte response as a result of the three tick exposures and feedings.