Cyclopenta-fused polycyclic aromatic hydrocarbons are a class of environmental PAH that has been recently identified. Many of these chemicals have been found to be more active that benzo(a)pyrene in tests for genetic toxicity using bacterial and rodent cells. Benz(l)aceanthrylene, a cyclopenta-polycyclic aromatic hydrocarbon related to benz(a)anthracene, and benzo(a)pyrene were compared for their activity to induce cytotoxicity and anchorage independent colony formation with normal human diploid fibroblasts. Both benz(l)aceanthrylene and benzo(a)pyrene were relatively non-cytotoxic to normal human diploid fibroblasts. However, benz(l)aceanthrylene was twice as active compared to benzo(a)pyrene over the concentration range examined as an inducer of anchorage independent growth. The ability of benz(l)aceanthrylene to induce anchorage independent colony growth in normal human cells in combination with its demonstrated ability as a mouse skin tumorigen suggests this PAH to be a potential multi-species carcinogen. (Copyright (c) 1990 Elsevier Science Publishers B.V. (Biomedical Division.)