Three court decisions reviewing medical peer review conducted in hospitals were discussed at length in part III of this article. In their opinions the courts gave at least tacit approval to the procedures followed in the hospitals, and they accepted that an evidentiary basis for adverse action against the physicians was present. But not all medical peer review in hospitals resulting in adverse actions is found satisfactory when challenged in court, and the most prominent litigation in the decade of the 1980s concerning medical peer review, Patrick v. Burget (1), is testimony to the potential for its perversion. Part II adverted to the potential for bias or lack of objectivity in assessing physician performance. Part I mentioned the problem of bias in the context of peer review of articles for publication and of research grant proposals. The objectives of Part IV are: (1) to examine the concern about bias in medical peer review and to indicate how it may be lessened, if not eliminated; (2) to address further the difficulty created by the relative lack of valid criteria to employ in medical peer review; (3) to review the extent of protection from liability afforded to participants in medical peer review; and (4) to describe the changes that should be anticipated in review of medical services in the future. Before addressing these subjects it is essential to remind the reader that medical peer review is not conducted primarily for disciplinary purposes; rather, its purpose is to evaluate the quality of care.(ABSTRACT TRUNCATED AT 250 WORDS)