Petroleum and synthetic hydrocarbons are used for the impregnation of paper-insulated power cables. To study the possible risk of skin cancer from such fluids a large series of hairless and a smaller series of SENCAR mice were exposed to long-term skin paintings with these fluids. The assayed fluids were two mineral oils, one C12-C20 polyisobutylene, two C14-20 alkylbenzenes, and one phenylxylylethane. The experiments were carried out according to three protocols: 1) A two-stage protocol using an initial single application of either 51.2 or 25.6 micrograms DMBA (7,12-dimethylbenz(alpha)anthracene) followed by long-term painting twice a week with 100 microliters of different concentrations of the fluids, with acetone as solvent; 2) a complete tumorigenesis protocol with long-term applications twice a week of the fluids alone or in various concentrations in acetone solution; and 3) a co-carcinogenesis protocol with long-term paintings with alternate applications twice a week of very small doses of DMBA and the fluid being studied. The animals were painted and/or observed for 18 months. Signs of skin toxicity, the occurrence of skin papillomas and carcinomas, swollen lymph nodes, and tumours and lesions in other organs found by autopsy were recorded. The results are documented in tables and in figures, and have been analysed by appropriate statistical methods. The oils were toxic to mouse skin, and had a certain general toxic effect indicated by a significantly increased death rate after long-term treatment with polyisobutylene, alkylbenzene A and PXE on hr/hr mice (see Appendix, p. 51), and there was also a tendency to increased amyloidosis. The fluids tested generally displayed a very low, non-significant tendency to induce skin tumours, mostly papillomas, and they are not significantly carcinogenic for skin. Generally, they do not enhance DMBA-induced tumorigenesis, with two exceptions (mixture of heavy mineral oils B/C after pretreatment with 25.6 micrograms, but not after 51.2 micrograms DMBA; and alkylbenzene A which very significantly enhanced DMBA-induced carcinogenesis, without enhancing tumorigenesis). Thus, in the concentrations used, the tested oils and fluids generally do not act as "promoters". On the contrary, most of them are so toxic that the number of tumours occurring after a single application of 51.2 micrograms DMBA is reduced by long-term applications of the oils and fluids, especially by higher concentrations, so in this respect they act in an antitumorigenic way. The fluids, except phenylxylylethane, were significant or suggestive inducers of malignant lymphomas in mice, either alone or in connection with initial treatment with DMBA.(ABSTRACT TRUNCATED AT 400 WORDS)