Expression of Fc gamma and Fc mu receptors on human peripheral blood T lymphocytes of two subsets with high (E early rosette forming presumably in vivo activated cells, TEe) and low affinity of E receptors (E late rosette forming presumable resting cells, TEl) was investigated. Different distribution pattern of T gamma and T mu cells in the both examined T cell subsets was found. Thus TEe and TEl subsets have been partially enriched in T mu and T gamma cells, respectively. Furthermore, the results obtained in the PHA-stimulated system have shown that Fc mu receptors do not function as the markers of T cell activation. However, in opposition to this finding Fc gamma receptors may be the early activation markers but only of T cells originally bearing high-affinity E receptors.