Sodium butyrate (NaB) can induce teratocarcinoma cell differentiation as retinoic acid (RA). However, the function of these two agents seems to be a little different [Kosaka et al., Exp Cell Res, 192:46-51, 1991]. F9 cells treated with NaB synthesize both tissue-type (tPA) and urokinase-type (uPA) plasminogen activator, though RA induces only tPA production. Urokinase-type PA is demonstrated to exist in association with membrane and to localize its activity to the close environment of the cell surface. This may cause the specific cell morphology and characteristics of differentiated F9 cells induced with NaB.