The quantitative expression of five properties of chemical carcinogen-induced, neoplastically transformed NIH strain 2 guinea pig fibroblasts was compared in cells possessing thousandfold differences in tumorigenicity. Plasminogen activator synthesis, sensitivity to lymphotoxin inhibition of cell proliferation, and the ability to induce a natural delayed tuberculin-type skin reaction in nonimmune syngeneic guinea pigs correlated directly with the number of cells required to produce a tumor. The most tumorigenic cells (10(2)-cell threshold dose) produced the most plasminogen activator, were most sensitive to lymphotoxin, and produced the greatest skin reactivity. Cells with a threshold tumor dose of 10(5)-10(7) cells exhibited the lowest expression of these properties. Fibronectin incorporation into an extracellular matrix was diminished in tumorigenic cells, as was anchorage-dependent growth; but neither diminished fibronectin incorporation nor the decreased anchorage requirement correlated quantitatively with the number of cells required to produce a tumor. The present investigation indicates that plasminogen activator synthesis, sensitivity to lymphotoxin, and the capacity of tumorigenic cells to induce natural delayed-type skin reactivity are among the factors that influence initial tumor growth. Plasminogen activator, an extracellular protease, may aid in the growth and spread of tumor cells in vivo by interfering with host fibrin deposition and by inactivating other host proteins such as lymphotoxin.