Public health has benefited greatly from control of some major sources of environmental pollution, but newer and more subtle types of pollution have led to a major loss of public confidence. This has often been aggravated by the tendency of authorities to issue quite improper reassurances in order to protect their own interests, as well as by the failure of medical experts to explain risks in an intelligible way. Control measures have mainly been focused on protecting individuals from conspicuous or hazardous levels of exposure. This may be grossly insufficient if--as with radiation--the dose-response curve is considered to be linear or threshold-free: it is then the total emissions which need to be controlled, since many people exposed to a small risk may generate a large total of cases, albeit with no conspicuous risk to any one person or group. Unfortunately it is generally impossible to measure these all-important low-dose effects. Environmental policy should take account of this uncertainty.