[en] Among sources of environmental pollution, pesticides contamination is wide spread and has become a source of concern. The organophosphorus pesticide, monocrotophos, is highly toxic compound and inhibits cholinesterase. It is very dangerous by all ways of exposure. Monocrotophos is used widely in Syria to control a variety of boring, chewing and sucking insects on various fruit and veditable crops. It is even, ellegally used to protect grapes in grape orchards from birds which is potentially hazaradous to both birds and the consumers of rthis crop. Monocrotophos is imported to Syria, and this is done according to a yearly plan to assess the amount needed of each pesticide. Such planning combined with variation in the incidence of pest infestation may lead to accummulation of pesticides from year to another, they become obsolete . Getting rid of such pesticides in the developing world is a problem, and Syria is no exception. There are various method of getting rid of obsolete pesticides ranging from containment to chemical methods of breaking down the pesticide. The present study aimed at assesing the feasiblity of using gamma radiation as a means to break down high concentrations of technical grade monocrotophos Several concentrations, 50, 200, and 400 mg/ml of technical grade monocrotophos were exposed to several doses of gamma radiation, namely, 0, 15, 45, 75, and 105 kGy. For each concentration tested percentages of monocrotophos breakdown increased with the increase of applied gamma radiation dose. However, the effect of gamma radiation dose was inversely related to monocrotophos concentration. The highest percentage of moncrotophos degradation was 60% and it was achieved by exposing 50 mg/ml of monocrotophos to 105 kGy of gamma radiation Breakdown products were identified using gas chromatography coupled with mass spectrometry GC-MS. Some identified products were dimethyl methyl phosphonate, phosphoric acid trimethyl and phosphoric acid dimethyl 1-methyl ethyl ester. 2-chloro-N-methylacetamide, an impurity arising during monocrotophos synthesis, only showed up following irradiation of moncrotophos with a dose equals or above 45 kGy. Toxicity of irradiated monocrtotophos and its breakdown products was assessed by injecting Albino rats with a fixed volume of various concentrations of radiation-exposed monocrotophos. Toxicity of monocrotophos and break down products decreased in a proportionate fashion to the increase in radiation dose. The LD50 for monocrotophos increased from 4-5 mg/kg/rat for non-irradiated monocrotophos to 108, 105, and 100 mg/kg/rat when a dose of 105 kGy of gamma radiation was applied to 50, 200, and 400 mg/ml of monocrotophos.(author)