Thirty male Sprague-Dawley rats received weekly injections of dimethylhydrazine for three months. They were subsequently laparotomized and tumors were palpated in 21 rats. The colonic tumor was removed and a fraction was autotransplanted into the wall of the transverse colon and a second fraction into the subcapsular space of the left kidney. The results demonstrated successful autotransplantation of colonic tumors in 13 of 21 rats (i.e., 62 percent). In 11 of the 21 rats (52 percent) the tumor grew in the left kidney. Of the various experimental methods proposed for the study of tumor metastases, the one described herein appears to be the first in which primary and secondary tumors were studied in the same individual, since dimethylhydrazine-treated rats usually develop more than one colonic tumor per individual. The model may be useful to monitor the effect of various drugs known to affect tumor growth, not only at the primary site, but also at the site of metastasis.