The invention provides a method for inhibiting an intracellular target in a cell with a bispecific antibody comprising contacting the cell with a bispecific antibody having a first Fv fragment with a cell-penetrating determinant and a second Fv fragment with an intracellular target-binding determinant under suitable conditions so that the first Fv fragment causes the bispecific antibody to enter the cell and the second Fv fragment binds the intracellular target in the cell and thereby inhibiting the intracellular target.