In a syngeneic tumor model by an indirect migration inhibition technique, using spleen cells from mice bearing large tumors (ATB-SC) no detectable amounts of migration inhibition factor (MIF) was found in response to either tumor cells or tumor extract. Although lymphokine production was suppressed, ATB-SC were able to respond to exogenous MIF and also to transfer a positive delayed foot-pad reaction (DFR) when co-inoculated with both forms of antigen into normal mice. These observations showed that in advanced stages of tumor development, when the ability of spleen cells to produce MIF toward tumor cells or tumor extract is lost, neither their capability to transfer a positive DFR not their responsiveness to MIF-rich culture supernatants were impaired.