Two classes of aminoacyl fucosides termed FL3 and FL4 were studied as possible markers of tumorigenic and metastatic potential in herpes simplex virus type 2 transformed rat cells. In the present study, clonal cell lines of transformed highly tumorigenic and metastatic (t-REF-G-1.1), weakly tumorigenic and nonmetastatic (t-REF-G-2.1), nontumorigenic (t-REF-G-2.0), and secondary nontransformed rat embryo fibroblast cells were labeled with [3H]fucose, and cell extracts were analyzed for ratio of radioactivity incorporated into FL3 and FL4. Results indicated that, in extracts from t-REF-G-2.0 and nontransformed rat embryo fibroblast cells, the ratios of FL4/FL3 were 5.78 and 5.71, respectively. In contrast, t-REF-G-2.1 cells exhibited a FL4/FL3 ratio of 1.45, while t-REF-G-1.1 cells exhibited a FL4/FL3 ratio of 0.74. In subclonal cell lines isolated from TPA-treated and mock-treated t-REF-G-2.1 cells, the FL4/FL3 ratios correlated with the tumorigenic and metastatic potential of these subclones in newborn syngeneic White Buffalo rats. These data suggested that alterations in fucose-labeled components can be used to predict the tumorigenic and metastatic potential of herpes simplex virus type 2-transformed rat cells.