The residual behaviour of Malathion, pirimiphos-methyl and profenofos applied to tomatoe field, at recommended rates was studied. This investigation was carried out in summer and in winter. Samples of tomato fruits and leaves were analysed by gas chromatography using N-P detector for residues determination. Initial deposits were higher on leaves than on fruits. Residue values at different days after applications revealed an initial fast degradation of the products, followed by a gradual elimination period. The dissipation pattern of three organophosphorus insecticides are presented . Mathematical equations, resulted from numerical analy-sis, shows that Malathion and pirimiphos-methyl follow a linear elimination pattern. However, the degradation behav-ior of profenofos fits a Gompertz and logisitic curves. Different equations presented can be used for forecast-ing the residual behavior of Malathion, pirimiphos-methyl and profenofos applied to tomato fields. Tomatos is a widely a grown crop in Egypt, it is culti-vated in different seasons. Fresh tomasto fruits are avail-able, in Egyptian markets throughout the year. Numerous pests attack tomatoes fields, mainly, white fly Bemisia tabaci, Some lepidopterous larvae, aphid (Aphididae) and grass hoppers (Acrididae). The most common of the insecticides used was Malathion for the control of aphids and white flies. Pirimiphos methyl was introduced as a substitute for ma/athion with an additional advantage of lower mammalian toxicity. Profenofos