Dihydro diols which are potential proximate carcinogens of the environmental agents benzo[b] fluoranthene (1), benzo[j]fluoranthene (2), and benzo[k]fluoranthene (3) were synthesized. The dihydro diols synthesized were trons-9,10-dihydro-9,10-dihydroxybenzofluoranthene (5), iraas-9,10-dihydro-9,10-dihydroxybenzo[j]- fluoranthene (6), and trans-8,9-dihydro-8,9-dihydroxybenzo[k]fluoranthene (7). In each case, the precursor to the dihydro diol was the corresponding ketone, e.g., 9-oxo-9,10,ll,12-tetrahydrobenzo[b]fluoranthene (21) for 5. The ketones were converted to the dihydro diols by reduction, dehydration, Prevost reaction, allylic bromination, dehydrobromination, and hydrolysis. The trans stereochemistry of the products from the Prevost reactions was established by comparison to the analogous derivatives prepared by osmium tetraoxide oxidation and by NMR. The UV spectra of the dihydrodiols 5-7 are presented.