There was considerable variation in susceptibility to bifenthrin in populations of the lygus bug (Lygus hesperus Knight) collected in the San Joaquin Valley as measured by the glass vial technique. The variation was similar to that found by the authors in a 1996 survey and was affected by pyrethroid use history and sampling date. Susceptibility of field populations in treated fields tended to decline immediately following an insecticide application and then gradually returned to pretreatment levels as the season progressed. However, if additional applications of another pyrethroid were made susceptibility continued to decline. The effect of another pyrethroid on the subsequent susceptibility of bifenthrin was examined in a large scale field trial. The results indicated that the impact on the susceptibility of lygus to bifenthrin was similar to that from an application of bifenthrin. This suggests that pyrethroids affect lygus susceptibility similarly. Various combinations of bifenthrin + endosulfan showed promising results against the less susceptible populations.