The purpose of the human monitoring program is to determine on a national scale levels of pesticide incidence in the general population and to assess changes in these levels. Such incidence reflects prior exposure from all sources and is important in understanding the ecological impact of pesticides pollution and in studying the human health effects of pesticides exposure. Exact measurement of man's total exposure to pesticides requires careful development and implementation of plans, the full cooperation of willing subjects, and adequate laboratory support--conditions which can be attained only in the controlled research situation and are not easily applicable to large groups. Previous human exposure to pesticides may be estimated from measurement of storage levels or excretion of these materials or their metabolites and from measurement of physiologic effects.