Two Fischer rats given injections of 1,2-dimethylhydrazine developed mucinous adenocarcinomas of the colon or jejunum which metastasized to the peritoneal and pleural cavities. Portions of metastatic peritoneal tumors were transplanted into weanling rats. The latent periods after intraperitoneal injection were reduced from 2-3 months in the first passages to 28–35 days by the fifth passages. At necropsy of these rats, tumors were found throughout the peritoneal and pleural cavities. Subcutaneous transplants grew progressively and metastasized to the lungs. Histology of transplanted tumors was similar to that of primary tumors, with some differences. Osteoid metaplasia was a feature of the jejunal transplants.