Montana Title 46. Criminal Procedure § 46-16-118. Alternate jurors

(1) The court may direct that one or more alternate jurors be selected in the same manner as principal jurors. The alternate jurors shall take the same oath as the principal jurors.

(2) Each party shall have one additional peremptory challenge for each alternate juror.

(3) Alternate jurors, in the order in which they are called, shall replace jurors who, prior to the time the jury arrives at its verdict, become unable or disqualified to perform their duties. An alternate juror may not join the jury in its deliberation unless called upon by the court to replace a member of the jury. An alternate juror's conduct during the period in which the jury is considering its verdict is regulated by instructions of the trial court. An alternate juror who does not replace a principal juror must be discharged after the jury arrives at its verdict.