Long term bioassays in animals cannot reliably forecast unknown potential but distant human risks, and especially cancer risks. The genetic, anatomic, physiologic, behavioral and environmental adaptations of rats and mice - the officially prescribed animals - are not relevant to humans. Even bioassay results for the two prescribed species are not mutually predictive. The dearth of human relevance is augmented by arbitrary and incongruous default assumptions, also officially prescribed for the conduct and interpretation of bioassays in rats and mice. Moreover, and contrary to publicized perceptions, bioassay results are freely evaded in the markup of regulations, with the imposition of arbitrary safety factors and the guided opinions of ad hoc appointed advisory committees. Regardless of bioassay results, actual regulations of unknowable distant risks end up allowing those minimum exposures that are still compatible with uses deemed necessary or useful for the common welfare. Thus it would seem sensible to do away with very costly long-term bioassays irrelevant to humans and whose results are anyway bypassed, and to focus regulations on short-term effects relevant to humans, and on transparent cost and benefit considerations toward minimizing useful exposures.