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Background: The German cockroach, Blattella germanica is a major hygienic pest and mechanical vector for path- ogenic agents in hospitals and residential areas. The development of insecticide resistance is a serious problem in controlling of this pest. Toxicity of four commonly used insecticides (permethrin, cypermethrin, malathion and chlorpyrifos) against two hospital- collected strains of the German cockroach was investigated. Methods: Topical bioassay methods were carried out for detecting insecticide susceptibility of adult male cock- roaches. For each insecticide, four to six concentrations resulting in >0% and