Ovarian carcinoma cell line HTBOA was established from a human ovarian anaplastic carcinoma. It has been proliferating stably since the beginning of culture 3 years ago after 91 passages. The cells were spindle like, oval, and polygonal in shape, and the nuclear chromatin was coarse in grain with many nucleoli, showing neoplasticity and pleomorphism. The cells proliferated rapidly, and the population doubling time was 24-28 hr. The chromosomes showed a wide distribution of aneuploidy, the mode was in the hypotriploid range, and many marker chromosomes were observed. Heterotransplantation was easy, and subcutaneous transplantation of 1 X 10(5) cells in nude mice forms a tumor that is histologically similar to the original anaplastic carcinoma. The most noteworthy characteristic of the cell line was that it caused granulocytosis in nude mice with carcinomas, and formed the colonies of granulocytes in an in vitro culture system. The cell line was considered to be producing a granulocyte colony-stimulating factor.