Resistance to the insecticides deltamethrin and malathion and the enzymes associated with metabolic resistance mechanisms were determined in four field populations of Aedes aegypti (L.) from western Venezuela during 2008 and 2010 using the bottle assay and the microplate biochemical techniques. For deltamethrin, mortality rates after 1 h exposure and after a 24-h recovery period were determined to calculate the 50% knock-downconcentration (KC₅₀) and the lethal concentration (LC_50,) respectively. For malathion, mortality was recorded at 24 h to determine the LC_50. For deltamethrin, resistance ratios of knock-down resistance and postrecovery were determined by calculating the RRKC₅₀ and RRLC₅₀, comparing the KC₅₀ and LC₅₀ values of the field populations and those of the susceptible New Orleans strain. Knock-down resistance to deltamethrin was moderate in the majority of the populations in 2008 (RRKC₅₀ values were between 5- and 10-fold), and only one population showed high resistance in 2010 (RRKC₅₀ >10-fold). Moderate and high postrecovery resistance to deltamethrin was observed in the majority of the populations for 2008 and 2010, respectively. There was significantly increased expression of glutathione-S-tranferases and mixedfunction oxidases. All populations showed low resistance to malathion in 2008 and 2010 with significantly higher levels of α-esterases for 2008 and 2010 and β-esterases for 2008.