This paper reports on a methodology for increasing proliferation and monoclonal antibody (mAb) production in hybridoma cultures. The 55-6 murine B cell hybridoma line (CD40 and CD19-deficient expression) was treated with increasing concentrations of lipopolysaccharide (LPS). Expression of CD69, CD40, and CD19 surface antigens on 55-6 cells did not show significant changes from untreated cells. The specific growth rate decreased at higher concentrations of LPS, but the monoclonal antibody production rate was highest at the highest LPS concentration assayed. These data are in agreement with the lowest growth rate found at this concentration of LPS. Furthermore, cells were cultured with anti-mouse surface immunoglobulin G antibody (anti-mIgG) plus LPS to find out whether LPS-derived signals and anti-mIgG stimuli are synergistic. CD69, CD40, and CD19 expression was greater than for either untreated cells (control culture) or cells stimulated with LPS alone. Moreover, LPS stimulation in combination with anti-mIgG enhanced both the growth rate and IgG2a production over the control culture and cells stimulated with LPS alone. Maximum antibody concentration increased almost 500% compared to the control and about 100% with respect to culture stimulated with LPS alone. The maximum specific IgG2a production rate was about 300% higher than in the control culture and about 30% higher than in culture stimulated only with LPS.