The technical literature on pesticides indicates there is extensive work being conducted and published on methods of analysis, extent of human exposure, symptomatology of poisoning and levels of pesticide residues in biological tissues and residues in all phases of our environment. A limited review of the literature establishes the need for greater emphasis on more properly controlled studies on the biological significance of pesticide residues. These studies should keep pace with the extensive development of chemical methodology and its applications. Since the general public is exposed to low levels of pesticides, biological studies must emphasize the possible effects of prolonged or repeated low-level exposure to pesticides on the functional aspects of sensitive physiological systems. Application of pharmacological methodology to these functional systems would facilitate a more sensitive evaluation of possible toxic effects.