The purpose of this study was the characterization of the different subsets of lymphocyte cells in dogs with subclinical ehrlichiosis in order to contribute to the knowledge of the immune response developed in the course of this disease. Thirty-eight dogs with subclinical ehrlichiosis and 15 unaffected dogs from two shelters in the area of Valencia (eastern Spain) were included in the study. The study of lymphocyte populations was made by flow cytometry. Monoclonal antibodies against CD3, CD4, CD8, and CD21 were used. Based on our results, the most common findings of the subclinical phase of canine ehrlichiosis were lymphocytosis, relative neutropenia, and a decrease in the neutrophil/lymphocyte ratio. Lymphocytosis in these dogs was from an increase of T lymphocyte counts. Tc cell counts in dogs with subclinical ehrlichiosis were higher than in healthy dogs. This rise in the number of Tc lymphocytes resulted in a reduced percentage of Th lymphocytes and in a decrease in the CD4/CD8 ratio.