Two new pyrethroids, ETOC and lambdacyhalothrin, showed considerable promise against organophosphorus-resistant adults of Culex tarsalis in laboratory tests. In field trials using nonthermal aerosols, applications of both compounds resulted in effective swaths of up to one-half mile. At the highest concentrations evaluated, residues on alfalfa foliage were less than 0.2 ppm at 1 h. Residues declined greatly by 24 h and could not be detected at 48 or 72 h.