The invention provides a natural killer cell, NK-92, modified to express an Fc receptor on the surface of the cell, such as CD16 (Fc.gamma.RIII-A), or other Fc.gamma. or Fc receptors. The modified NK-92 cell can be further modified to concurrently express an associated accessory signaling protein, such as Fc.epsilon.RI-.gamma., TCR-.zeta., or to concurrently express interleukin-2 (IL-2) or other cytokines. Additional methods are disclosed for various assays, assessments, and therapeutic treatments with the modified NK-92 cells.