The ability of 18 different hydrocarbons to induce and promote morphological transformation and to inhibit intercellular communication in primary Syrian hamster embryo cells in culture have been studied. The compounds were: the n-alkanes octane, nonane, decane, undecane, dodecane and tridecane; the iso-alkanes 2-methylheptane, 2-methyloctane and 2-methylnonane; the naphthenes 1,2-dimethylcyclohexane, 1,2,4-trimethylcyclohexane and tert-butylcyclohexane; the aromates 1,2-dimethylbenzene, 1,2,4-trimetylbenzene and tert-butylbenzene; and the alkenes 1-octene, 1-nonene and 1-decene. None of the hydrocarbons induced morphological transformation of Syrian hamster embryo cells. When the hydrocarbons were incubated together with benzo(a)pyrene, enhancement of the transformation frequency was observed for the naphthene 1,2-dimethylcyclohexane and the iso-alkanes 2-methylheptane and 2-methyloctane. None of the n-alkanes, alkenes or aromates enhanced the transformation frequency induced by benzo(a)pyrene. The alkane tridecane and the iso-alkanes 2-methyloctane and 2-methylnonane reduced intercellular communication in the primary Syrian hamster embryo cells.