The expansion of criminal sanctions into areas previously reserved for administrative and civil enforcement has resulted in an increase of parallel civil and criminal suits. These suits raise constitutional, discovery, and estoppel issues, although there is no per se rule against parallel suits. In U.S. v Kordel, the U.S. Supreme Court held that use of evidence obtained through civil discovery to gain criminal convictions was neither a violation of due process nor a departure from proper standards in the administration of justice. However, conflicts may arise between Federal civil discovery, which intends the fullest mutual disclosure, and more restrictive criminal procedure. In a leading case, Campbell v. Eastland, the Supreme Court refuse to allow a civil plaintiff, also being prosecuted for tax fraud, to procure evidence under civil discovery rules to which he was not otherwise entitled. In the wake of Campbell, a number of courts have indicated the necessity of preventing parties from exceeding the bounds of criminal discovery in the interest of procedural integrity. Conflicts also arise in parallel suits concerning fifth amendment rights, because the right is broader in criminal proceedings. Some courts have concluded that parallel suits pose a threat to fifth amendment rights and that the defendant may require special judicial protection. The potential effects of parallel proceedings on a defendant's right to a fair trial are diverse. The burden of defending two suits may hamper a defendant's right to a fair trial; civil discovery and the defendant's conduct in the civil trial may reveal his criminal trial strategies; and assertion of the fifth amendment in criminal proceedings may weaken a civil case. However, due to Kordel's holding, courts have not generally ruled that parallel suit problems constitute due process violations. Moreover, courts have consistently declined to apply double jeopardy to parallel suits. Defendants may seek various remedies to alleviate parallel suit problems, including stays of the civil action, protective orders, and use of the All Writs Act and collateral order doctrine. Footnotes are included.