We intend to study other plasma cell tumor lines, using velocity cell sedimentation to determine if there is a population of cells which are responsible for oncogenesis in these tumors. It will be of great interest to determine if these cells can be identified by a common characteristic. We are pursuing studies on the immune response of tumor-bearing animals treated with the long-acting forms of progesterone and testosterone. It is planned to look at the immune cell system during the induction of the plasma cell tumor by mineral oil and during the growth phase of the transplanted plasma cell tumor. It is also of interest to determine if the plasma cell tumor elaborates a factor that can block the immune response to a second antigen, such as sheep red blood cells, either at the primary or at the secondary response.