This study is a continuation of our previous work demonstrating the potentiating activity of TFX on cyclophosphamide-induced immunosuppression. Mice primed with TFX subsequently received cyclophosphamide and antigen and their B cell responses were evaluated with an aid of antigen-specific and reverse plaque forming cell assay. Cyclophosphamide-dependent inhibition of immunoglobulin synthesis was significantly stronger in mice pretreated with TFX than in controls. However, the synergistic immunosuppressive action of TFX with cyclophosphamide was evident only when polyclonal but not specific humoral response was studied.