Various populations of Lygus bugs, Lygus hesperus, and cotton aphid, Aphis gossypii, were collected during 1996 from cotton fields and alfalfa fields next to cotton throughout the San Joaquin Valley and bioassayed for insecticide resistance. Significant resistance was found in 52% and 39% of Lygus populations for Capture (pyrethroid) and Metasystox-R (organophosphate), respectively. Significant resistance was also found in cotton aphids, 83% of populations resistant to Capture, 71% of populations resistant to Thiodan (chlorinated hydrocarbon), and 42% of populations resistant to Lorsban (organophosphate). These three categories of insecticides have been used for many years for control of cotton pests in the San Joaquin Valley and so it is not surprising that insecticide resistance is increasing. This explains in part the erratic control growers are achieving and points out the need for greater dependence on nonchemical methods of cotton pest control to extend the useful life of insecticides.