Objective To investigate the abnormal expressions of light chain immunoglobulins kappa (Ig?) and lambda ( Ig?) in multiple primary malignant tumors (MPMT) in elderly patients. Methods The expressions of Ig? and Ig? in specimens obtained from multiple malignant tumors in 21 elderly patients were investigated. Immunohistochemical staining was performed with mouse antihuman Ig? and Ig? monoclonal antibodies. Among 21 patients with multiple primary malignant tumors, the first tumor which occurred in the digestive tract was detected in 20 patients. In 17 patients first and second tumors were found to occur in the digestive tract. In 21 patients with MPMT the relationship between the expressions of light chain immunogloblin and survival time was analyzed. Results Positive staining of Ig? and/or Ig? in specimens from the first and/or second tumor tissues was found in 16 patients(76 2%). Statistic analysis showed that there was close relationship between the expression of Ig? and that of Ig? in the tissues from double tumors ( P