A cytogenetic survey was conducted on personnel exposed to petroleum exhaust fumes (vapour and smoke at automobile workshops). The incidence of chromosomal aberrations (CAs) in this population was evaluated. A total of 1.15 +/- 0.22 aberrations were encountered in the exposed group as compared with 0.47 +/- 0.12 aberrations in the age matched controls. The increase in CAs in the exposed group was highly significant (P < 0.01, test of variance). A strongly positive correlation between increasing exposure duration and a higher incidence of CAs was apparent. No stratification for a higher incidence of CAs on the basis of smoking and/or alcoholic habits could be made in the exposed group.