Enzyme-inducing and cytotoxic effects of wood-based materials used as bedding for laboratory animals were studied in a cell culture system. Mouse hepatoma cell line, Hepa-1, was exposed to acetone extracts of hardwoods (alder and aspen), softwoods (pine and a mixture of pine and spruce) and cellulose materials. Cytotoxicity and induction of cytochrome P450IA1 (aryl hydrocarbon hydroxylase) and aldehyde dehydrogenase were measured. Both softwood and hardwood extracts were shown to contain inducers of these enzymes. Pine appeared to be the most potent inducer and softwoods more potent than hardwoods. The softwoods and alder were clearly more cytotoxic than aspen. The two bleached cellulose materials were found to contain inducers of aryl hydrocarbon hydroxylase. Unlike the wood beddings, the extracts of the cellulose materials were not found to be toxic to the cells. Hepa-1 cell culture system was found to be a rapid and sensitive method for screening and comparative purposes.