Cancer cells of the effusions were decreased by chemotherapy, but this did not always indicate a good clinical course. 2) When the clinical condition was fairly good, the percentage of lymphocytes predominated in the pleural effusion. 3) When the clinical conditions became rather critical, there was an increase in the number of macrophage. 4) The cytologic findings were observed prior to the time the clinical symptoms became manifest. 5) The percentage of lymphocytes and macrophages in pleural effusions was not related to the percentage of lymphocytes and monocytes in peripheral blood.