Measurements of penetration, excretion and total metabolism of radiolabelled cypermethrin were made from individual Heliothis virescens collected from cotton fields in Texas and Louisiana where less than adequate control with insecticides had been observed in 1992. On average, no dramatic differences in pharmacokinetic profiles were observed between these pyrethroid-resistant strains when compared with a reference, susceptible colony. Frequency histograms suggest that the disposition of cypermethrin is variable among individuals within these populations. For most collections, this variation was within the range of response seen in the susceptible, LSU strain and therefore, would not seem to account for the levels of pyrethroid resistance expressed by the field-collected strains. In some strains, however, our data suggest the presence of individuals, at low frequencies, that express delayed penetration and enhanced metabolism and excretion of this insecticide, but the degree to which these varying levels affect insecticide resistance is not clear.