The expression of both high-affinity E receptor (EhR) to sheep erythrocytes and CD2-11.3 epitope on activated human T lymphocytes suggests that these two structures may be functionally identical or closely associated. Therefore the aim of the present work was to determine if the CD2-11.3 epitope is involved in the early E rosette formation. The ability of normal and phytohaemagglutin (PHA)-activated human T lymphocytes to express the CD2-11.3 epitope and to form early E rosettes (T cells with EhR) was studied simultaneously. The partial divergence of CD2-11.3 expression on T lymphocytes from the ability of these cells to form early E (Ee) rosettes was found. The results indicated that the expression of CD2-11.3 epitope alone is insufficient to form the Ee rosettes by activated T lymphocytes, yet it may facilitate this phenomenon in the presence of EhR. The above data clearly show that the CD2-11.3 epitope is functionally closely associated although not identical to EhR. Accordingly, it seems that these two structures may co-adhere to the appropriate ligand. Thus it is possible that the CD2-11.3 epitope, as well as its established role in activation signalling, may also act as a co-adhesion molecule.