First and third instar larvae and adult males of susceptible (S) and pyrethroid (PY) resistant (R) strains of tobacco budworm (TBW), Heliothis virescens (F.), were bioassayed with different insecticides using a glass liquid scintillation vial technique. Resistance to the PYs cypermethrin and fenvalerate was observed in first instar larvae of all R strains. Low or no tolerance by first instar larvae was observed to the organophosphates profenofos, acephate, and methyl paratmon or the cyclodiene endosulfan. Only one R strain, Uvalde, showed resistance to the oxime carbamate thiodicarb. The combination cypermethrin plus thiodicarb seemed to be synergistic only against the Uvalde strain. Overall, the resistance spectra to different insecticides were approximately the same for different R TBW strains. Chordimeform synergized all insecticides tested against first instar larvae. The synergism was variable for different insecticides between strains. Differences in tolerance to cypermethrin observed between R adult males and first instar larvae showed that resistance does not manifest equally in all developmental stages of TBW. Tests with cypermethrin and methyl parathion showed higher resistance in third than in first instar larvae, indicating the presence of both target site and metabolic resistances. On the other hand, no stage showed tolerance to the ± isomer organophosphorothiolate acephate. The use of 3-way combination of cypermethrin, chlordimeform, and piperonyl butoxide gave nearly 2,000-fold synergism at the LC-90 level and improved the control of PY-R third instar TBW larvae to such an extent that toxicity was only about 6-fold less than that of the cypermethrin only against the susceptible strain. Based on the information presented, a general approach for managing PY resistance in TBW is proposed.