In 1994, the Australian cotton farmer must use a wide range of costly chemicals to harvest a profitable crop. These chemicals vary significantly in their degree of hazard. Some chemicals (e.g. the organophosphates) directly threaten humans and other animals, because of their effect on nervous function. Others, such as the pyrethroids, are innocuous to humans, but toxic to fish. Still others, such as the esters of 2,4- dichlorophenoxyacetic acid (2,4-D) used on crops like wheat grown in rotation with cotton, are of concern because of their mobility in air and their possible effect on nontarget crops such as grapevines or cotton. But currently, most attention is focussed on those that have potential environmental effects, such as endosulfan