Deltamethrin and cypermethrin are extensively used insecticides to which humans are widely exposed. The present study is designed to analyze the effects of these two pesticides on HePG2 cell lines and on differentiated 3T3-L1 and C2C12 cells with respect to the expression of small ubiquitinlike modifiers (SUMO) and SUMO-conjugating enzyme UBC9. Treatment of HePG2 cells with either deltamethrin or cypermethrin caused elevated mRNA levels of SUMO 2 and 3 as well as UBC9. This was associated with elevated nitric oxide and nitric oxide synthase mRNA levels and decreased NADPH levels. Differentiated 3T3-L1 cells treated with either deltamethrin or cypermethrin led to increased mRNA levels of inflammatory cytokines IL-Iβ and IL-6, indicating that these pesticides promote the inflammatory response. These observations are significant since previous studies reported that UBC9 and SUMO isoforms are upregulated in many types of cancers and hence the extensive use of these pesticides is a concern.