Abs to IL-2 and IL-4 can inhibit the in vivo growth of LSA but not that of P815 in nude mice. Groups of four nude mice injected with LSA (A) or P815 (B) subcutaneously were treated on the same day and were treated thereafter for 16 days with intraperitoneal injections of normal rat IgG (R-IgG; control) or with a combination of MoAbs against IL-2 and IL-4, on alternate days. On the seventeenth day, tumors were surgically removed and weighed. The vertical bars represent the mean ± SE values of tumor weight. Statistically significant differences (P < .05) from the control values have been indicated with an asterisk. It should be noted that, in one LSA-bearing nude mouse treated with anti–IL-2 and anti–IL-4 Abs, the tumor completely failed to grow, and the mouse survived indefinitely.