Effect of unautoclaved or autoclaved contact bedding materials (mixed hardwood, white spruce, white pine, and red cedar shavings) on pentobarbital sleeptime and liver:body weight ratios was assayed in young DBA/2J and C57BL/6J male mice. Analysis of variance indicated that autoclaving the bedding did not alter either parameter in either strain. Within strains, data were pooled and analyzed for bedding effects. Sleeptimes of DBA/2J male mice on mixed hardwood or white spruce bedding were not significantly different, but were significantly longer than sleeptimes of mice on white pine or red cedar bedding. Sleeptimes of DBA/2J mice on white pine were significantly longer than mice on red cedar. Sleeptimes on C57BL/6J male mice on each bedding were significantly different with the following rank order:mixed hardwood greater than white spruce greater than white pine greater than red cedar. In both strains, liver:body weight ratios of mice on red cedar bedding were significantly increased compared to mice on white pine, white spruce, or mixed hardwood beddings. The results of this study indicated that autoclaving these beddings did not alter pentobarbital sleeptimes or liver/:body weight ratios and that softwood beddings differ in their abilities to alter pentobarbital sleeptimes.