Pesticides have useful and harmful effects. on the one hand they are useful for controlling pests that damage crops on the other hand they can cause damage to man and beneficial organisms. some sub-lethal effects of pesticides were studied in raboits and birds with a vie.l to identifying characteristic biochemical responses that ney oe useful for the monitoring of exposure to suo-lethal levels in the field. new zealand white raobits, wild rabbits, starlings and house sparrows were used in this study. seven pesticides were used: demeton-s-methyl (dsm), chlorpyriphos, chlorferll1inphos, triazophos, pirimicarb, methiocaro and permethrin. blood was collected before dosing, and at 2, 6, 24, 48, and 72 hours after the treatment fr00\ the ear vein of raooits and from the brachial vein of birds. enzyme activities were assayed in the p-iasne or serum samples ootained. the assays used were glutamate oxaloacetate transaminase (got), glutamate dehydrogenase (gdh), soroitol dehydrogenase (sdh), -glutamyl transferase (-gt), and cholinesterase (che). when the level of certain enzymes had increased such as ,got and -gt, the animals were sacrificed and the liver was studied histologically using iight and electron microscopy. in addition to laooratory studies, field work was carried out at boxworth (camoridgeshire) on wild rabbits and house sparrows with the organophosphorus pesticide demeton-s-methyl. in iaboratory studies an increase in plasm3 and serum got and 'i'-gt ievels were found in all animals treated with the previous pesticides. the ievel of serum che increased in birds after treatment with permethrin. using iight microscopic studies, iiver cell enlargement occured in :-1ew zealand white rabbits following treatment with dsm, chlorpyriphob and chlorfenvinphos, and in wild rabbits treated with dsm. blood got ievels were elevated in ali these animais. the proportion of cells that were binucleated increased in wild rabbits treated with dsm. in starlings treated with methiocarb, fatty accumulation occured in the liver 24 hours after exposure. electron microscopic studies showed the development of dark staining ..'esicles in the liver of new zealand white raboits and wild raobits treated with pesticides. these may have oeen due t accumulation of bile m3terials or lipofuscin. in a field in..'estigation of wild rabbits and house sparrows, it was found that animais vary in their response after exposure to dsm. it was also concluded that the measurement of plasma or serum got, sdh, gdh and '(-gt activities may be useful parameters for assessing exposure and sub-iethal effects of pesticides on the wildlife.