Recent reports 1-3 have proposed that T-lymphocytes (thymus derived) could be distinguished from B-lymphocytes (thymus independent) by examining their features under the scanning electron microscope. T-cells were designated as having relatively smooth surfaced cells, whereas B-cells had "hairy" surfaces with many microvilli. We have examined this hypothesis in congenitally athymic "nude" mice, animals lacking T-cells,4 and have not been able to confirm these reports. We have found that lymphocytes from nude (nu/nu) mice are indistinguishable from lymphocytes obtained from normal littermates (NLM) and CBA/J mice. We have found that in all the murine lymphoid tissue examined, including nude, the complete gamut of cell surface types, ranging from smooth to "hairy" are present. Our studies indicate that the proposed T- and B-cell classification based upon human surface morphology under the scanning electron microscope is questionable in a mouse model. It is presently unclear whether the smooth lymphocytes seen in nude mice are immature B-cells, pre-T-cells, or another unidentified population of cells.