The sweet potato whitefly (Bemisia tabaci Gennadius) is increasingly gaining importance as a significant pest worldwide on various crops, primarily cotton. Studies in the Imperial Valley, California, have shown that the whitefly populations have become resistant/crossresistant to the three synthetic pyrethroids, permethrin, cypermethrin, fenvalerate, and the two organophosphates, oarathion and monocrotophos. The level of resistance that has developed appears to be dependent on the local pesticide-use regime. Limited data suggests that the level of resistance was relatively stable during a 12 month period when the colony was maintained in the laboratory. Based on the data obtained, it appears that the resistant whitefly populations may be more localized than hitherto expected. The results and interpretations of these studies on resistance are discussed in light of the problem of whitefly management in cotton.