Since the scope of the defendant's constitutional right to discover or introduce evidence protected by an evidentiary privilege depends on whether the privilege favors the government, those privileges favoring government should be differentiated from other privileges so that a fair relationship exists between the defendant and the government in criminal cases. When a new procedure or evidentiary rule improperly tilts the adversarial balance in the government's favor, a limitation should be imposed upon the government's right to invoke such privileges. Three guiding principles for assessing the defendant's constitutional right to introduce evidence protected by evidentiary privileges are: (1) defendant should have the constitutional right to introduce evidence protected by a privilege designed to assist the government in performing one of its essential functions when the evidence will affect the trial outcome; (2) in most circumstances defendant should have a constitutional right to introduce evidence protected by a privilege if the privilege would not exclude comparable evidence offered by the government; and (3) no privilege should be invoked that would deprive the defendant from cross-examining a government witness. 221 footnotes.