The production of leukocyte migration inhibition factor (LIF) from lymphocytes after stimulation with 3 M KCl soluble tumor and normal mucosa extracts was investigated in 30 patients with laryngeal carcinoma at different development stages and in 30 normal donors. The experiments were performed in heterologous and autologous systems. In heterologous systems 3 M KCl tumor extracts induced LIF production by heterologous lymphocytes from patients in 91% of the cases, and normal mucosa extracts induced LIF production by heterologous lymphocytes from patients in 73% of the cases and from normal donors in 90% of the cases. In autologous systems 3 M KCl tumor extracts induced LIF production by autologous lymphocytes from the same patients in 65% of the cases, whereas the normal laryngeal mucosa extracts induced LIF production by the same autologous lymphocytes in the 6% of the cases. The high positivity percentage of the test in heterologous systems could be related to differences in the major histocompatibility complex. The 65% test positivity in autologous systems using tumor extracts could be related to the presence of tumor associated antigens.