We have recently shown the expression of lymphoid early developmental markers, including CD104, Thy 1, CD1a, Pgp-1 and TdT, by the cells constituting atopic dermatitis skin infiltrates. To further characterize the cellular phenotypes we used an indirect immunoperoxidase assay to analyze sections from two atopic dermatitis lesion skin biopsies using the following as first step monoclonal antibodies (MAB): anti-CD34, CD2, CD5 and CD7. CD34+ mononuclear cells and endothelial cells were identified. A strong immunoreaction was observed for the T-lineage marker CD2 and CD5, but a poor reaction, if any, was seen for the CD7. Since CD34+ marrow and blood cells are currently believed to be the major source of the hemopoietic precursors, our data provide further substantial evidence supporting the hypothesis that the atopic dermatitis skin cell infiltrate represents an ongoing T-lineage in situ differentiation process regulated by the skin epithelial microenvironment. The observed defective expression of the CD7 antigen requires further investigation for its confirmation as a possible constant feature in atopic dermatitis.