Lymphocytosis indicates increased numbers of circulating lymphocytes. Pathologic lymphocytosis occurs in chronic inflammation, recovery from acute infection, lymphocytic leukemia, and hypoadrenocorticism. Lymphocytosis usually indicates a strong immune stimulus of some chronic duration from a bacterial infection, viremia or immune-mediated disease. Lymphocytic leukemia may or may not be accompanied by lymphocytosis. Lymphocytosis not associated with disease occurs with physiologic leukocytosis, in healthy cats from excitement, immature age-related responses in young puppies and kittens, and sometimes following vaccination.