Opponents of public health and environmental regulations often try to "manufacture uncertainty" by questioning the validity of scientific evidence on which the regulations are based. Though most identified with the tobacco industry, this strategy has also been used by producers of other hazardous products. Its proponents use the label "junk science" to ridicule research that threatens powerful interests. This strategy of manufacturing uncertainty is antithetical to the public health principle that decisions be made using the best evidence available. The public health system must ensure that scientific evidence is evaluated in a manner that assures the public's health and environment will be adequately protected.