Transforming growth factors alpha and beta (TGF-alpha and TGF-beta) isolated from normal mouse kidney induced gross morphological changes in rat urothelial cells maintained in organ culture. These morphological effects are similar to those observed after long-term treatment of rat bladder organ cultures with the carcinogen N-methyl-N-nitrosourea (MNU) or the promoting agents sodium saccharin and sodium cyclamate. Cultures were treated continuously with 5-25 micrograms/ml of Bio-Gel P-30-purified TGF containing both TGF-alpha and TGF-beta between days 1 and 14 in culture, or with 5 micrograms/ml from days 28 to 42. Controls received 1-10 ng/ml epidermal growth factor (EGF) or control medium. Untreated controls retained a normal urothelium throughout the period of study. Mature superficial-type cells covered most of the surface and less mature forms appeared on the cut sides and damaged areas where cells followed the normal pattern of urothelial differentiation. EGF at 5 and 10 ng/ml caused necrosis of the entire urothelium but at 1 and 2 ng/ml had minimal effects on histology and scanning electron microscopical appearance up to 14 days in culture. Crude P-30-purified TGFs induced a series of dose-related changes from 4 days, which were maximal at 8 days and persisted or decreased between 8 and 14 days. These included hyperplasia, loss of epithelial polarity, hyperchromasia and elongation of basal cells between the overlying cell layers to reach the culture surface. Scanning electron microscopy showed the appearance at the culture surface of immature cells with gross surface abnormalities including large numbers of blebs, stubby microvilli and long pleomorphic microvilli. Immature cells on the sides of the culture and in damaged areas developed similar features. At crude TGF doses of 10 micrograms/ml many superficial cells were rounded, some became cystic and epithelial necrosis was observed. Cultures treated with h.p.l.c.-purified TGF-beta at 80 ng/ml in the presence of 2 ng/ml EGF showed similar effects to those treated with 5 micrograms/ml P-30-purified TGF. Fully differentiated cultures treated from 28 to 42 days with crude TGF, showed changes similar to those seen in early cultures. However, histological changes, particularly basal cell elongation were more widespread and there was an abnormal development of globular processes between the membrane ridges of mature superficial cells. Neither crude TGF nor EGF stimulated growth in soft agar of isolated epithelial cells from freshly killed rats or organ cultures pretreated for 7 days with EGF or TGF.(ABSTRACT TRUNCATED AT 400 WORDS)