AbstractThe pyrethroid insecticide permethrin was tested for its ability to induce structural chromosome aberrations (CA) in human lymphocyte cultures and CHO cells, in order to confirm the clastogenic effect of itself and to compare the response of the two different cell types. Permethrin was tested in the range of 50–200 μg/ml in human lymphocyte cultures and in the range of 20–100 μg/ml in CHO cells. In both lymphocyte and CHO cultures, assays were performed in the absence and in the presence of a rat liver activation system (S9 mix). In the absence of S9 mix, two experiments with different duration of the treatment were carried out. Permethrin induced CA in both cultures when it was evaluated in the absence of a metabolic activation system. The activity of a given concentration of permethrin seemed to be decreased more by the reduction of the time of exposure than by the presence of S9 mix. Aberrations induced by permethrin were mainly chromosome‐type aberrations in both cultures. Thus, permethrin can be characterised as an S‐phase independent clastogenic agent. The response of both lymphocyte and CHO cultures was similar, indicating that both systems showed the same sensitivity for detecting the clastogenicity in vitro of permethrin. © 1994 Wiley