C3H-AvyfB female mice were tested on bedding consisting only of low-resin pine and on bedding of pine plus cedar shavings. Tumor occurrences were similar in both groups of animals, with a slightly lower incidence and slightly higher average age for mammary gland tumors in the females on bedding of pine plus cedar. From these results, the high incidence of cancer in the C3H-AvyfB strain could not be attributed to the routine use of cedar shavings in the bedding material.