Peripheral lymphocytes of ten normal, healthy subjects were assayed simultaneously for spontaneous 3H-thymidine flash labelling and erythrocyte, active erythrocyte and erythrocyte antibody complement rosette formation. Spontaneous blastogenesis of T lymphocytes is significatively higher than that of B cells. The majority of T lymphocytes incorporating 3-H-thymidine are active E rosette-forming cells.