AbstractCytolysis was obtained with plasma membrane fractions prepared not only from cytolytic T cells, but also from nonimmune lymphoid cells and, moreover, from cell lines of nonlymphoid origin displaying no lytic ability. Furthermore, no relationship exists between the genetic specificity of T cell‐mediated cytolysis and the activity of membrane preparations. If anything, it appears that certain cell types may be unusually sensitive to membrane‐mediated cytolysis. Our observations argue against a mechanistic relationship between T cell‐mediated and membrane‐mediated cytolysis.