Although specific for T lymphocytes, E-rosette methodology is limited in that it provides for visual identification and manual enumeration of sheep erythrocyte - T lymphocyte complexes by light microscopy only. Measurement of SmIg for identification and enumeration of B lymphocytes is also limited in that other cellular populations may express SmIg and/or bind Ig via receptors for the Fc portion of IgG resulting in false Ig positivity.