The "HEW Committee to Coordinate Toxicology and Other Related Programs" has designed a study to establish the biologic consequence of ingestion of asbestos. NIEHS has the responsibility for effecting these protocols. One aspect of the study is to determine if asbestos can act as a co-carcinogen, specifically in the gastrointestinal tract. 1,2-Dimethylhydrazine (DMH) and methylazoxymethanol (MAM) are known intestinal carcinogens; however, the dose required to produce a relatively low incidence (15 plus or minus 5%) of colon cancer is not known. The objective of this study is to derive this information and, in addition, to critically evaluate any neoplasm produced as to location, size, and morphology.