[Objectives]  Cytochrome P450 monooxygenase (P450) and glutathione S-transferase (GST) are important enzymes for the degradation of exogenous toxins in eukaryotes and play key roles in insecticide resistance in insects. In a previous study we found that the transcriptional levels of the Epsilon GST (GSTe1) and P450 CYP9 (CYP9J40) genes were upregulated in a parathion-resistant strain of Culex pipiens quinquefasciatus. We here explore the temporal and spatial expression pa-tterns of these two genes in order to further elaborate their biological functions. [Methods]  Real-time PCR and in situ hybridization were used to explore the temporal and spatial expression patterns of the two genes. [Results]  Real-time PCR showed that the transcription levels of GSTe1 and CYP9J40 in the parathion-resistant strain of C. p. quinquefasciatus were 4.2 and 1.9-fold higher, respectively, than those of a susceptible strain. These two genes had similar expression patterns over the mosquito life cycle; expression was low in larvae, increased in pupae, and peaked in female adults, whereas expre-ssion in male adults was the same as that in larvae. In situ hybridization demonstrated that both genes were expressed in muscle, the digestive tract, and ovary. CYP9J40 was, however, expressed in a greater range of tissues, including the brain and thoracic ganglion, than GSTe1. [Conclusion]  The observed changes in expression levels during development and the expression of these genes in a wide range of tissues imply that, in addition to insecticide resistance, GSTe1 and CYP9J40 play a role in other metabolic processes, such as female development.