Multiple intraperitoneal injections of various normal sera into BALB/c mice inoculated intraperitoneally with Landschütz ascites tumour cells abrogated the development of ascitic syndrome in almost all the animals. In a large proportion of the survivors solid intraperitoneal tumours developed, composed of characteristic ascites tumour cells engulfed and encapsulated in connective tissue. The effect of serum on the development of the solid tumour was diminished if the donor had been immunized against mouse IgG. Inoculated animals treated with serum hyperimmune against mouse IgG showed accelerated ascitic tumour growth. Cyclophosphamide or arabinosylcytosine strongly inhibited growth of solid tumours. Simultaneous administration of arabinosylcytosine and its antagonist cycloheximide did not interrupt tumour growth.

Landschütz tumour cells in the ascitic form injected subcutaneously into BALB/c or ICR mice produce solid tumours which grow progressively in most ICR mice but regress in nearly all BALB/c mice. Solid tumours in the peritoneal wall (produced by intraperitoneal inoculation of ascitic cells and treatment with normal serum) grew in both strains, but were more invasive in ICR mice. Surgical interference in BALB/c mice with these tumours, allowing adhesion of tumour to skin or subcutaneous fascia, resulted in cessation of tumour growth or regression.