This study was conducted for the induction and propagation of plasmacytomas in BALB/c mice. A total of 170 BALB/c female mice were injected intraperitoneally with pristane or paraffme oil in an attempt to produce plasmacytomas and to follow up the immunocompetance of these mice during the 16th months of the experiment. In the first experiment, 20 mouse were injected with pristane. Oil granuloma developed nearly 6 months later with perfuse peritoneal ascites. Cytological and histological examination of ascites cytosmears and paraffme wax fixed oil granuloma sections revealed the appearance of precancerous lymphoblastoid cells and at later stages, a typical plasmacytoma cells in both ascites cytosmears and histological sections. Propagation of two cell specimens produced an epithelioid and rounded types monolayer which bear the characteristics of the original plasmacytoma ascitic cells. Two types of cells were characterized on the basis of immunoglobulin (Ig) secretion properties by using anti-mouse immunoglobulin fluorescence isothiocyanate (FITC) conjugate, which stain the Ig secreting cells. Further, characterization included 8- azaguanin adaptation for hypoxanthine guanosine phosphoribosyl transferase (HGPRT) negative selection. Hypoxanthine, aminopterin, thymidine (HAT) sensitivity and chromosomal picture all revealed a considerable similarity to classical plasmacytomas features. In the second experiment a 150 mouse were injected with 0.5 ml paraffme oil divided into three successive doses. Groups of 10 mice were sacrificed at 1, 2, 3, 4, 6, 8, 10, 12, 16 months intervals. Peripheral blood samples were taken to test the leukocyte phagocytic function toward bacterial cells as well as the spleen were removed and single cell suspensions were prepared and, examined for proliferative response toward bacterial lipopolysaccharide (LPS) mitogen; in attempt to evaluate the immunostatus of these mice during the development and progression of plasmacytomas. Moreover, mice developed ascites were canulized and ascites fluid was removed aseptically for studying the immunosuppressive properties of ascites fluid on normal allogeneic mice spleen cells. The results of 10 separate experiment of both the in-vivo testing of splenocyte blastogenic response and in-vitro effect of ascites on normal mouse spleen cells as well as peripheral leukocyte phagocytic function provided an interesting pattern for the behavior of the immune system during the development and progression of tumor in these mice.