Murine lymphoma models are commonly used to test the efficacy of idiotype-based vaccines for B-cell lymphoma prior to human trials. Mouse survival has been used as an indirect measure of the tumor response to the vaccine. In this study, we describe a multiparameter flow cytometric (MPFC) assay that enables direct assessment of the tumor at the inoculation site and detection of lymphoma metastases. In initial experiments, we show that 38C13 mouse lymphoma cells expressed an aberrant phenotype compared to normal splenocytes. The combination of CD45, CD19, B220 and an anti-idiotypic antibody (S1C5) along with a sequential gating technique defined the 38C13 cells with high sensitivity and specificity. The specificity of the MPFC assay for 38C13 lymphoma cells was greater than a gating strategy using light scatter and idiotype antibody binding. The MPFC assay was used to monitor 38C13 tumor kinetics in the C3H/HeN mouse and demonstrated tumor growth at the inoculation site and metastases to the lymph nodes and bone marrow. The presence of 38C13 metastases in lymphoid organs and bone marrow predicted by the MPFC assay were confirmed by histology and immunohistochemistry (IHC). The MPFC assay will enable investigators to monitor 38C13 lymphoma tumor response to individual vaccines or other lymphoma therapy prior to clinical trials. Furthermore, the MPFC concept could be readily applied to other models of human B cell lymphoma.