“…Although the results of these biochemical and biophysical investigations have often provided strong circumstantial evidence implicating one particular dihydrodiol, additional evidence that this dihydrodiol is more biologically active than other dihydrodiols derived from the same hydrocarbon has usually been sought from test systems in which dihydrodiols are expected to be metabolically converted in situ into the related vicinal diolepoxides. Such studies on mutagenicity (Malaveille et al, 1975(Malaveille et al, , 1977Wislocki et al, 1976) and on the abilities of non-Kregion dihydrodiols to induce malignant transformation in mammalian cells (Marquardt et al, , 1977b and to initiate tumours in mouse skin (Chouroulinkov et al, 1976(Chouroulinkov et al, , 1977Slaga et at., 1976;Levin et at., 1976) have been useful in helping to identify those dihydrodiols that are the precursors of the vicinal diol-epoxides involved in the metabolic activation of benzo[a]pyrene and 7-methylbenz[a]anthracene. Attention has now been turned towards the metabolic activation of other hydrocarbons, and efforts are beinig made to identify the dihydrodiols concerned in the activation of, for example, benz [a]anthracene (BA) (Wood et at., 1976(Wood et at., , 1977aanthracene (DMBA) (Moschel et al, 1977;Vigny et al, 1977b;Ivanovic et al, 1978) and 3-methylcholanthrene (King et al, 1977;Thakker et al, 1978 (II), are known to be converted into a variety of K-region and non-K-region dihydrodiols by rat-liver preparations (Boyland & Sims, 1964, 1965Sims, 1970;Tierney et al, 1978b (Marquardt et al, 1974) are described.…”