Cypermethrin-piperonyl butoxide formulations (1:1, 1:5, 1:10) were evaluated in a laboratory wind tunnel against colony reared, susceptible adult Culex quinquefasciatus mosquitoes. Scourge (4% resmethrin:12% piperonyl butoxide) was used as the standard for comparison. Based on the LC90 data, the 3 cypermethrin-piperonyl butoxide formulations were 2.6-3.7x more toxic than Scourge 24-h posttreatment.