421 U.S. 35 (1975)
The State of Wisconsin maintains an Examining Board of practicing physicians that issues medical licenses and enforces standards against professional misconduct, fee splitting, and unauthorized practice under names other than the licensed name.1 Appellee Duane R. Larkin, a Michigan resident, obtained a Wisconsin medical license in August 1971 under a reciprocity agreement and maintained a Milwaukee practice performing abortions.2 On June 20, 1973, the Board notified Larkin that it would hold a closed investigative hearing on July 12, 1973, under Wis. Stat. Ann. § 448.17 to determine whether he had engaged in proscribed acts, with the possibility of warning, reprimand, or referral for criminal or revocation proceedings.3
Larkin filed suit in the United States District Court for the Eastern District of Wisconsin under 42 U.S.C. § 1983 seeking preliminary and permanent injunctive relief against enforcement of the statutes and the investigative hearing.4 The district court denied a temporary restraining order.5 The Board conducted the investigative hearing on July 12 and 13, 1973, at which numerous witnesses testified and Larkin's counsel was present throughout; counsel was later informed Larkin could appear to explain the evidence.6 On September 18, 1973, the Board noticed a contested hearing for October 4, 1973, to determine whether Larkin's license should be temporarily suspended under Wis. Stat. Ann. § 448.18(7).7
The district court granted a restraining order against the contested hearing, concluded a substantial federal question existed, and requested a three-judge court.8 The Board instead held a final investigative session on October 4, 1973, and issued findings of fact, conclusions of law, and a decision determining probable cause to believe Larkin had violated criminal provisions and engaged in unprofessional conduct, directing referral to the Milwaukee County District Attorney for revocation and criminal proceedings.9 On November 19, 1973, the three-judge court held § 448.18(7) unconstitutional as a due process violation and enjoined its enforcement; judgment was entered January 31, 1974.10 Appellants appealed and the Supreme Court noted probable jurisdiction on June 10, 1974.11 The district court later modified its judgment on July 25, 1974, to withdraw the declaration of unconstitutionality and enjoin enforcement of the statute only against Larkin.12
Whether the Wisconsin medical examining board's combination of investigative and adjudicative functions in proceedings against a licensed physician violates due process?13
A fair trial in a fair tribunal is a basic requirement of due process. This requirement applies to administrative agencies. The combination of investigative and adjudicative functions does not in itself create an unconstitutional risk of bias. A presumption of honesty and integrity attaches to adjudicators. Due process forbids the combination only when a realistic appraisal shows the risk of actual bias is intolerably high.14
No. The Board conducted the investigative hearing on July 12 and 13, 1973, at which Larkin's counsel was present throughout. The Board later issued findings of probable cause after a final investigative session on October 4, 1973, before any contested hearing occurred. This sequence matches the accepted administrative practice upheld in FTC v. Cement Institute. It is also consistent with NLRB v. Donnelly Garment Co. The established facts contain no specific evidence that the Board was prejudiced or unable to decide on the basis of evidence presented at an adversary hearing.15
The board's sequence of investigative and adjudicative functions does not violate due process.16
Whether a district court may declare a state statute unconstitutional in an order granting a preliminary injunction protecting a plaintiff during litigation?17
A district court should not declare a state statute unconstitutional when granting a preliminary injunction. The only question presented is whether the plaintiff has raised serious constitutional questions and shown that enforcement pending final hearing would inflict irreparable injury.18
No. The three-judge district court initially declared section 448.18(7) unconstitutional and enjoined the Board from utilizing the section against any licensee in its January 31, 1974 judgment. The only proper inquiry under Mayo v. Lakeland Highlands Canning Co. was whether serious questions existed and irreparable harm would occur. The court later modified the judgment on July 25, 1974, to limit the injunction to Larkin alone.19
The district court's initial declaration that the statute was unconstitutional exceeded its authority at the preliminary-injunction stage.20