A thymic lymphoma was found in a 14-month-old Holstein steer. Use of antisera applicable to paraffin-embedded sections showed that the tumor cells were of T-cell lineage. Although the cells were characterized histologically by the presence of irregular nuclei, electron microscopic examination disclosed that they were cleaved. Although nuclear convolution and cleavage are important in the subtyping of some human lymphomas, these characteristics may not be related to the immunophenotype of the tumor cells bovine lymphomas.