1.  Generally

The Sixth Amendment provides that "[i]n all criminal prosecutions, the accused shall enjoy the right…to have compulsory process for obtaining witnesses in his favor."{footnote}U.S. Const. amend. VI.
See also Ark. Const. Art. 2, § 10; Wis. Const. art. I, § 7.{/footnote}  This provision is made applicable to the states through the Fourteenth Amendment.{footnote}Washington v. Texas, 388 U.S. 14 (1967).{/footnote}

In Washington v. Texas,{footnote}388 U.S. 14, 23 (1967).{/footnote} the Court held that states may not arbitrarily prevent a criminal defendant from introducing testimony by a witness who is physically and mentally capable of testifying to events within his personal knowledge which are relevant and material to the defense.{footnote}388 U.S. at 23.{/footnote}  The Court struck down a Texas law that prohibited accomplices from testifying for one another.  The Court wrote:

The right to offer the testimony of witnesses, and to compel their attendance, if necessary, is in plain terms the right to present a defense, the right to present the defendant’s version of the facts as well as the prosecution’s to the jury so it may decide where the truth lies.  Just as an accused has the right to confront the prosecution’s witnesses for the purpose of challenging their testimony, he has the right to present his own witnesses to establish a defense.  This right is a fundameental element of due process of law.{footnote}388 U.S. at 19.{/footnote}

The right to present relevant testimony is not without limitation, but "’may, in appropriate cases, bow to accomodate other legitimate interests in the criminal trial process.’"{footnote}Rock v. Arkansas, 483 U.S. 44, 55 (1987) (quoting Chambers v. Mississippi, 410 U.S. 284, 295 (1973); Mancusi v. Stubbs, 408 U.S. 204 (1972); Hughes v. Mathews, 576 F.2d 1250 (7th Cir.), cert. dismissed, 439 U.S. 801 (1978).{/footnote}  The Sixth Amendment merely "prevents the adoption of broad arbitrary limitations" on defense evidence.{footnote}Myers v. Frye, 401 F.2d 18, 21 (7th Cir. 1968).{/footnote}

2.  Constitutional Violation Found

The following types of defense evidence have been held, based on the Compulsory Process Clause, improperly excluded: an accomplice’s testimony,{footnote}Washington v. Texas, 388 U.S. 14 (1967).{/footnote} the defendant’s own hypnotically-enhanced testimony,{footnote}Rock v. Arkansas, 483 U.S. 44, 55 (1987).{/footnote} testimony as to another persons’s confession to the crime charged,{footnote}Chambers v. Mississippi, 410 U.S. 284, 295 (1973).{/footnote} character testimony as to a government witness excluded as a discovery sanction,{footnote}United States v. Davis, 639 F.2d 239 (5th Cir. 1981).{/footnote} and expert testimony on "homosexual panic" as explanation for the defendant’s state of mind in a murder case.{footnote}Parisie v. Greer, 671 F.2d 1011 (7th Cir. 1982).{/footnote}

3.  No Constitutional Violation Found

The exclusion of the following types of defense evidence has been held not to violate the Compulsory Process Clause: evidence of intoxication offered to negate criminal intent,{footnote}Montana v. Egelhoff, 116 S.Ct. 2013 (1996).{/footnote} a defense witness excluded under a rule of procedure requiring pre-trial disclosure of witnesses,{footnote}Taylor v. Illinois, 108 S. Ct. 646 (1988) (where identity of defense witness was not disclosed to the prosecution as requested during pretrial discovery, court’s exclusion of witness as sanction did not violate compulsory process clause).{/footnote} expert testimony as to eyewitness idenification{footnote}Moore v. Tate, 882 F.2d 1107, 1111 (6th Cir. 1989).{/footnote} and the battered woman syndrome.{footnote}Tourlakis v. Morris, 738 F. Supp. 1128, 1137 (S.D. Ohio 1990); Fennell v. Goolsby, 630 F. Supp. 451 (E.D. Pa. 1985).
Contra Thomas v. Arn, 728 F.2d 813, 815 (6th Cir. 1984), aff’d, 474 U.S. 140 (1985) (Jones, J., concurring).{/footnote}