LA31-NRK and B77-NRK are established cell lines that were normal rat kidney cells transformed with temperature-sensitive mutant (LA31) and wild-type Bratislava 77 (B77) of Rous sarcoma virus. It is recognized that many transformation-induced changes differentiate between normal and transformed cells. Morphology and four parameters of transformed cells such as saturation density, anchorage independence, plasminogen activator, and colony stimulating factor were used as indicators to observe the effect of human alpha interferon on the growth of NRK, LA31-NRK and B77-NRK. The results show that interferon could neither reverse the transformed cells to normal fashion nor change their behaviors or cause release of protease.