HuPBL-SCID mice were used to explore how they would response to human tumor cells of 801/MLC. Living 801/MLC cells appeared to be fetal to the the mice due to the production of human TNF. The huPBL-SCID mice did not generate any noticeable amount of specific human immunoglobulin either by single immunization with living 801/MLC cells or by repeated immunization with irradiated 801/MLC cells. Our preliminary experiments with huPBL-SCID mice showed that such chimeras would be a very useful models for tumor immunological researches.