Clones of four Gross virus-induced murine lymphoblast lines, established in culture from C3H mice, were selected for detailed study of the relationships among in vitro growth parameters, oncogenicity, and agglutination with concanavalin A. The four clones were intially divided into two groups on the basis of their in vitro growth properties. Two strains, N-811 and H-111, had low saturation densities, low cloning efficiencies, and slower doubling times; the other two strains, L-274 and L-258, had higher saturation densities, higher cloning efficiencies, and faster doubling times. The ability of the strains to produce tumors in mice correlated with their in vitro growth properties: L-274 and L-258, with their high saturation densities and high cloning efficiencies, were more tumorigenic in mice than were N-811 and H-111 cells with their lower saturation densities and lower cloning efficiencies. All strains were agglutinable with concanavalin A; however, the agglutination response did not correlate with saturation density or oncongenicity.