The safety claim was central to the clinic’s positioning during Niehans’s lifetime. The claim rests on the false premise that fetal xenogeneic tissue is immunologically inert in human recipients. Documented adverse events in the fresh-cell-therapy literature include anaphylaxis, encephalitis, transmission of slow viruses and prions, and severe inflammatory reactions; these are among the principal grounds for the eventual prohibition of fresh-cell therapy within recognized medicine in Switzerland and Germany. The clinic published no adverse-event registry during Niehans’s career.