Organized psychiatry has recently begun to define limits to expert testimony. The American Psychiatric Association filed an amicus brief in the case of Barefoot v. Estelle urging legal curtailment of psychiatric testimony as to future dangerousness and prohibition on Constitutional grounds of expert psychiatric testimony solely based on hypothetical data. The Supreme Court refused relief on both questions. Psychiatric testimony to ultimate questions at law is limited by the inherent contextual variables of psychiatric clinical and experimental knowledge and practice. A forensic science model for psychiatric participation with explicit psychiatrically defined limitations is proposed using competence to stand trial as an example.