Pesticides almost always occur in mixtures with other ones. The toxicological 
effects of low-dose pesticide mixtures on the human health are largely unknown, 
although there are growing concerns about their safety. The combined 
toxicological effects of two or more components of a pesticide mixture can take 
one of three forms: independent, dose addition or interaction. Not all mixtures 
of pesticides with similar chemical structures produce additive effects; thus, 
if they act on multiple sites their mixtures may produce different toxic 
effects. The additive approach also fails when evaluating mixtures that involve 
a secondary chemical that changes the toxicokinetics of the pesticide as a 
result of its increased activation or decreased detoxification, which is 
followed by an enhanced or reduced toxicity, respectively. This review addresses 
a number of toxicological interactions of pesticide mixtures at a molecular 
level. Examples of such interactions include the postulated mechanisms for the 
potentiation of pyrethroid, carbaryl and triazine herbicides toxicity by 
organophosphates; how the toxicity of some organophosphates can be potentiated 
by other organophosphates or by previous exposure to organochlorines; the 
synergism between pyrethroid and carbamate compounds and the antagonism between 
triazine herbicides and prochloraz. Particular interactions are also addressed, 
such as those of pesticides acting as endocrine disruptors, the cumulative 
toxicity of organophosphates and organochlorines resulting in estrogenic effects 
and the promotion of organophosphate-induced delayed polyneuropathy.