Toxicological and pharmacological effects arise when chemicals interact with biophysiological functions in discrete cell types. There is a continuing need to screen novel compounds for their potential therapeutic effects, and once these have been "discovered" to understand their molecular actions, as the basis of using such compounds safely and for rational drug design. Pharmacology now uses all of the sophisticated molecular research techniques that are available for the development of safer and more efficacious drugs. Histochemistry has been usefully applied to developing new drugs (and...