The heterotransplantability of HOTHC line (human anaplastic thyroid carcinoma) into the subcutis of BALB/c nude mice and the biological properties of grafts were discussed. (1) The HOTHC line showed high transplantability, and 1 x 10(4) cells produced anaplastic carcinoma (giant cell type) containing the colloid-like substance. (2) The grafted tumors grew rapidly and the mice were dead within 2 months after transplantation. (3) The number of leukocytes (neutrophils) of mouse peripheral blood increased as the tumor size increased, and the leukocyte count returned to a normal value after removal of the tumor. (4) The conditioned media of HOTHC line formed colonies of granulocytes (neutrophils) on soft agar. These phenomena revealed that HOTHC is a granulocyte-colony stimulating factor-producing line. (5) The conditioned media of HOTHC line showed promoting-effect on neovascularization on the chorioallantoic membrane.