Pesticide effects on nontarget organisms have been a source of worldwide contention and concern for more than a decade and are the basis for most legislation aimed at controlling or prohibiting the use of specific pesticides. For example, the present list of pesticides to undergo Rebuttal Presumption Against Registration (RPAR) numbers 45. All of these are being reviewed because of their effects on nontarget organisms, most with reference to man. Only 13 were triggered by criteria relating to reduction in nontargets and endangered species (birds and feral mammals) while the rest hinged on laboratory animal effects listed as oncogenicity, fetotoxicity, mutagenicity, teratogenicity, and reproductive effects. Thus, most pesticides undergoing RPAR have untoward effects on laboratory animals that are translated as potential effects on man, the ultimate nontarget.