Using quantitative polymerase chain reaction (QPCR), the relative transcriptional levels of cytochrome c oxidase subunit 3 (COS) were studied in Aedes aegypti in response to treatment with acetone, permethrin, and fipronil. The transcriptional levels of CO3 were significantly (P < 0.05) higher in acetone-treated Ae. aegypti compared with that in untreated samples. Using ribosomal L24, heat shock protein (HSP), and actin as reference genes, relative transcription levels of CO3 in acetone-treated Ae. aegypti were 2.88 ± 0.38-, 2.60 ± 0.60-, and 3.24 ± 0.70-fold higher, respectively, compared with that in untreated mosquitoes. Transcriptional levels of CO3 were induced significantly higher (6.54 ± 1.22-, 4.62 ± 0.74-, and 9.47 ± 3.71-fold, respectively) by permethrin at LD₁₀ compared with acetone (P < 0.05). Taken together, our results suggest that overexpression of CO3 is tightly regulated in Ae. aegypti in response to xenobiotic treatment.