The pesticides for which the most expensive data on use are currently available are those applied in agricultural settings. Similarly, the majority of information on pesticide detections in ground water has been collected for pesticides used within predominantly agricultural areas. The available data indicate that the pesticides detected most frequently in ground water are also those used widely in agriculture, namely, the triazines and acetanilides. Some of the more heavily used insecticides and fumigants, such as aldicarb, DBCP, and EDB, have also been among the pesticides detected most often in ground water. For those detected, pesticide detections in ground waters generally become more common with greater use and greater analysis. Direct relations between pesticides detection frequencies and use become more evident when data on pesticide use are aggregated over smaller areas. When pesticide use is assessed at comparatively large spatial areas, low use is typically associated with low frequencies of pesticide detection in ground water, while high use is associated with a broad range of detection frequencies. A comprehensive review of published information on the distribution of pesticides in ground water indicates that pesticides from various chemical classes heve been detected in ground water. Many of these compounds are commonly present at low concentrations in shallow ground water immediately beneath agricultural land. Information on pesticides in ground water is not sufficient to provide either a statistically representative view of pesticide occurence in ground water across various countries or an indication of long-term trends or changes in the severity or extent of this contamination over time.This is largely due to wide variations in analytical detection limits, site selection procedures, and other design features among studies conducted in different countries at different times. Past approaches have not been well suited for distinguishing "point source" from "no-point source" pesticide contamination. Among the variety of natural and anthropogenic factors examined, those that appear to be most strongly associated with the intensity of pesticide contamination of ground water are the depth, construction, and age of the sampled wells, the amount of the recharge (precipitation or irrigation), and the depth of the tillage, proximity to surface water (gw/sw interactions) are responsible for a huge number of detections, since surface run-Off...