The susceptiblity of some filed strains of TriboLium castanewn and SitophiZus orsae, collected from different i gypt to phosphine, was studied in compa rison to a laboratory strain of each insect species. Results revealed that the tolerance ratios for T.castanewz at the LC.T99.9—levels and 26÷1 C varied from 0,78( for . Cairo strain) to 2.24 times (for Menoufia strain).Atç÷JC the . tolerance ratios varied also at the LC.T99.9—Zevels from 0.92 (fOr Cairo sh’din) to 5.23 times (for Shark ia ,tىeJ2 raىn). The tolerance ratios for S. oryaae at the L.C.T99.9—Zevels and 26÷lt’ varied from 0.57 (for Darnietta filed strain) to 1.82 times (for Kalyubia filed strain). At c1t’ the tolerance ratios varied from 0.75 (for Kalyubia svrain) to 2.12 times (for Behera strain), in comparison with the laboratory strain at the LC.T99.9—levei. Such differences in the susceptiblity of the filed strains of the two insect species to phosphine could result in the failure of control program and should be given full consideration during practical fumigation.