Bioassays were performed in order to detect the susceptibility of Aedes aegypti to the chemical insecticides temephos and cypermethrin. The results showed that this species is susceptible to temephos and presents resistance to cypermethrin.The strategies for controlling the principal vector of dengue, Aedes aegypti, are based on the utilization of chemical and biological products, integrated with environmental management programs. In Brazil, the programs that aim to control Aedes aegypti mainly utilize chemical insecticides, among which organophosphates (OP) and pyrethroids (P) are prominent. These programs require constant monitoring.The numbers of dengue cases are rising every year, and different factors influence this increase. Resistance to chemical products may favor an increase in the mosquito populations, thereby resulting in increases in the numbers of dengue cases. 1,4 For this reason, it is important to perform periodic monitoring of the susceptibility to insecticides of the populations implicated in the transmission of this disease. 3 This study presents data on the susceptibility of a population of Aedes aegypti in the city of Curitiba, State of Paraná, for the first time. This population was submitted to two chemical insecticides: temephos (organophosphate) and cypermethrin (pyrethroid). The resistance ratio was compared with the data for the standard colony at the Centers for Disease Control and Prevention (CDC).Immature specimens were collected from different districts of Curitiba between January and April 2003.Aedes aegypti was only found in the sample from the Uberaba district, in an artificial breeding ground (automobile wreckage in a scrap metal yard). This was the only population originating from Curitiba utilized in the susceptibility tests.The lineage utilized for making the comparison was the Rockefeller CDC. The insecticides utilized in the bioassays were temephos, "Temephos Fersol 1G" (granulated, 1%), and cypermethrin, "Cynoff 400 Pm" (powder, 25%). These products were diluted in mineral water to prepare the standard solutions with the same concentration of 50 ppm of active ingredient.The process for the bioassays followed the standards of the World Health Organization (WHO). 5 The results were submitted to Probit analysis. 2 The following criteria were utilized for determining the resistance: if the mortality rate was greater than or equal to 98%, the sample was considered to susceptible; if the mortality rate was 80 to 97%, the response was checked by repeating the experiment; and if the mortality rate was less than 80%, the sample was considered to be resistant. 5 A total of 750 larvae were analyzed in relation to cypermethrin and 700 in relation to temephos, in-