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Abstract: Background: German cockroach or Blattella germanica is a common pest in residential buildings, which not only disseminates various microorganisms but it is one of the most important causes of allergies in infested areas. The goal of this study was to determine the susceptibility of German cockroaches of Tehran to some pesticides. Methods and Materials: Blattella germanica collected from residential areas were exposed to different concentrations of Coopex, Ficam, Diazinon and Fenitrothion using contact method in 2003. Probit analysis was performed for estimation of KT50 and KT90. The statistical Package of GLIM 4 was used for data analysis. Results: The results of this study showed that the KT50 of 2.5% Actellic, 0.5% Ficam, 5% Diazinon, 1% Fenitrothion, 0.5% Fenitroithion and 0.25% Fenitrothion were 88, 129, 61, 54, 71 and 146 min respectively. Also the times required for KT90 estimated to be 218, 415, 94, 143, 185 and 284 min accordingly. Conclusion: This results indicated that the susceptibility of German cockroaches of Tehran to Coopex, Ficam and Actelic was relatively low, so to find more suitable chemicals and to combat probable resistance, further experiments with different chemicals and even different control measures should be considered.