The effects of surface sources, ozonized surface films, and surface dissolution, on the nature of plastic flow in NaCl single crystals were studied using etch pit and birefringence techniques. Slip steps increase in depth and become rounded as the slip band broadens. This is also often accompanied by a bending of the steps as much as 3° off ⟨100⟩. These effects are explained in terms of both internal and surface cross‐slip mechanisms. Ozonization of NaCl for short periods restricts the action of surface sources and for longer times provides barriers to the egress of dislocations. The ``Suzuki effect'' (formation of a work‐hardened surface layer) is found to depend upon the existence of a multiplicity of surface sources such as is produced by polishing on wet silk. Cross‐slip of screw dislocations at the surface is found to be greater and flow more homogeneous when the surface is dissolved during deformation. This is proposed as a likely mechanism to explain the ``Joffe effect'' when atmospheric variables are eliminated.