It takes 24 months to induce preinvasive carcinomas in the urinary bladder of dogs as reported in the literature. The transplantation of chemically induced carcinomas has never been successful. Therefore, it was looked for methods which enable a shortening of the latency period and to transplant such tumors. 12 of 22 female beagle whelps were injected transurethrally with fast polymerizing plastics and then they have been treated subcutaneously with ortho-aminodiphenyl, formylaminonitrofurylthiazole or with the two carcinogens together. The dogs have been controlled by endoscopy, cytology and histology every 4 weeks. The first invasive urothelial carcinomas were observed 13 months after starting the treatment. Totally 7 carcinomas of the bladder and 3 in the pelvis of the kidney were found. It was possible to cultivate tumor material in tissue culture, gained by biopsy transurethrally. The transplantation of tissue culture material into nude mice was successful in 19 of 23 animals. In 2 of 10 beagles tumors started to grow transiently after transplantation of tissue culture cells. In the bacterial mutagenicity test (Ames) and in animals ortho-aminodiphenyl was neither mutagenic nor carcinogenic. However, it was cocarcinogenic if used together with formylaminonitrofurylthiazole.