Labelled analogue of Dibenzo[a,i]pyrene, a polycyclic aromatic hydrocarbon (PAH) with potent carcinogenic activity. Dibenzo[a,i]pyrene was shown to induce DNA adduction, tumorigenicity as well as Ki-ras oncogene mutations in strain A/J mouse lung. Dibenzo[a,i]pyrene has been shown to be present in cigarette smoke condensate and in automobile exhaust gas in small quantities.