Many polycyclic aromatic hydrocarbons (PAHs) have been identified as cancer-inducing chemicals for animals and/or humans, Also, there is sufficient evidence that exposures in the occupational settings are carcinogenic or probably carcinogenic to human. Engine exhaust and used engine oils are major PAH sources in engine repair workshops and traffic. Analysis of micronucleus (MN) in exfoliated buccal cells is a sensitive method for monitoring genetic damage in human populations. In our study, we used three different occupational groups (Group 1; engine repair workers, Group 2; taxi drivers, Group 3; traffic police) and two controls (Control I for Group 1 and Control II for Group 2 and Group 3) for the exposed groups, We analysed MN frequencies in exfoliated buccal cells and compared the exposed groups (Group 1; n = 34, Group 3; n = 17, Group 3; n = 15) and subjects not occupationally exposed to PAH (Control I; n = 28, Control II; n = 20). The mean (+/- S.D.) MN (%) frequencies in exfoliated buccal cells from Group 1 and Control I were 0.07 +/- 0.05 and 0.05 +/- 0.04, respectively (p > 0.05; Table 2). The mean (+/- S.D.) MN (%) frequencies in exfoliated buccal cells from Group 2, 3 and Control II were 0.12 +/- 0.05, 0.10 +/- 0.05 and 0.03 +/- 0.03, respectively (p < 0.0001, p < 0.05; Table 2) Smokers and nonsmokers do not differ with respect to the incidence of MN in all groups. (C) 1999 Elsevier Science B.V. All rights reserved.