In esophageal cancer patients, pneumonia in an early (20%) and a late (3.5%) period, pythorax except for leakage (8%) and pulmonary tuberculosis (1.4%) were observed characteristically through the post operative course. Changes in cellular immunity through the course were indicated with remarkable depression of PHA stimulation index (s.i.) and T cell number. The lowest values during 5-year survey were observed 2 weeks after surgery. Especially, cases with post operative pulmonary infections had low PHA s.i. and low T cell number for long time, different from cases without them. As regards T cell subsets, both helper T and suppressor T decreased dramatically early after surgery and helper T kept in low value for long time, in contrast to suppressor T returned to normal range gradually, and then H/S ratio also depressively changed. Therefore, suppressive immunity after surgery must result in pulmonary infections and cause critical conditions. Cases with well reacted lymphocytes indicated high 5 year survival rate (40%).