Lymphoid neoplasms of abdominal cavity origin were found in two cows infected with bovine leukemia virus (BLV). Case 1 was a 3-year-old Japanese Black cow affected with a B-1 B cell lymphoma. Case 2 was a 14-year-old Japanese Black cow that developed a γδ T cell lymphoma. Immunohistochemically, CD79a-positive lymphoma cells were observed in case 1, whereas CD3-, WC1- or perforin-positive ones were seen in case 2. Despite the expression of CD5 in both lymphomas, the reactivity was surface or cytoplasmic in case 1 and surface membrane in case 2. Erythrophagia by tumor cells of both cases was considered to be due to the fact that their normal counterparts were more primitive forms than conventional lymphocytes.